RAID 10 not as fault tolerant as RAID 5 ??? unlikely...RAID 5 is used when capacity cannot be sacrificed for the increased data protection of RAID 10. Yes, RAID 0+1 is horrible, and should be avoided as mentioned in other posts. RAID 10 sets will absolutely rebuild faster than a RAID 5 in almost all situations. With the dirt cheap pricing of modern large capacity drives, I can think of almost no situation where RAID 5 is preferable to RAID 10. The flaw is in the way hard drives die, and parity. I was going to type out a long explanation, but this link covers it well.
I strongly urge any home user not to use RAID 5 ( or any other parity form of RAID ). RAID 5 is antiquated and left over from the days when cost vs capacity was a major concern. RAID 10 also dosen't require as expensive of a controller card.
And remember if you do insist on RAID 5 to never use it as a system disk. The parity overhead from the many small writes an OS performs is far too great a penalty.
I'm not trying to start a fight, just trying to educate on the flaws of parity.
The drives in my 2 drive RAID 1 array are 100% readable as normal drives by any SATA controller.
With any other RAID configuration you are dependent on both remembering the proper settings, performing the rebuild properly and most importantly, finding a compatible controller.
Until the manufactures decide to standardize, the system you have in place to protect your data could have you waiting days to access your data.
I am planning to add a RAID 5/6 array for home theater usage, but the business documents are staying on the RAID 1 array.
That's my acronym for it. It also describes my desire for it.
RAID = Redundant Array of Independent Disks.
AIDS = Array of Independent Disks, Striped.
"RAID" 0 has very few legitimate uses. If you value the data stored at all, and have any care at all about uptime, it's inappropriate. If all you want is an ultra-fast 'scratch' disk, it is appropriate. Before ultra-large drives, I used a RAID-0 of 9 GB, 10k RPM SCSI drives as my capture and edit partition for video editing, and that's about it. Once the editing was done, I wrote the finished file back out to DV tape, and transcoded to something more manageable for computer use, and storage on my main ATA hard drive.
[quote]"Higher quality RAID 1 controllers can outperform single drive implementations by making both drives active for read operations. This can in theory reduce file access times (requests are sent to whichever drive is closer to the desired data) as well as potentially doubling data throughput on reads"[/quote]
Its not the best place to post here I know, but as a home user with a 1tb 0+1 pata array on a promise fastrack (on a budget) I was thinking of looking on ebay for a reliable replacement controller with the above characteristics, but dont know what series cards are both inexpensive for a second user now and fit an x32 pci.
> but as a home user with a 1tb 0+1 pata array on a promise fastrack (on a budget) I was thinking of looking on ebay for a reliable replacement controller with the above characteristics, but dont know what series cards are both inexpensive for a second user now and fit an x32 pci.
saying you currently have a 0+1 array i assume you have at least 4 drives, probably 4 500gb drives
since 0+1 provides the speed of raid0 with the mirroring of raid1 i'm not sure what you're looking for. if you went for a straight raid1 solution your system would see 2 500gb volumes instead of 1 1tb volume.
and not sure what you mean by x32 pci, just a regular pci slot? if you're talking about PCIe they only go to x16 and can't say i'm aware of any 'reasonable' card that uses more than x8
and performs as quoted from the article, because my promise controller is good but still a home class controller. Just i dont know the enterprise segment at all and I thought some of these guys would.
if you search that page you will see x32 doesn't show up anywhere on it
i'm going to assume you just mean 32-bit PCI which is standard which is what practically every motherboard manufactured today has at least one of
but still i can't answer your question about which PCI (no need to say 32-bit, it's assumed) raid controllers support IDE drives with enhanced read speed, sorry
I gave up on RAID "for protection" a long time ago. I tried everything from software RAID to on-board 1 and 5, and to $300 cards with controllers and on-board RAM and 5 hard drives. It is not worth the hassle for home use or even small business, period. I absolutely agree with that article from Pudget computers. I had more problems due to raid controllers acting up than hard drive failures. RAID will nor protect you against directory corruption, accidental deletion and infections - things that happen A LOT more often than hard drive failures. RAID adds level of complexity that involves extra maintenance and extra cost.
My current solution is two external FW or USB drivers. I run two redundant Retrospect backups every 12 hours, one right after another that backs up my storage drive plus one at night that mirrors the drive to another. It's probably an overkill but I'll take it over any RAID5 any time: three separate drives, three separate file systems - total protection against file deletion, directory corruption and infections (the external drives are dismounted between backups. I do the same on Macs and PCs.
I still may use RAID0 for scratch and system disks for speed, but my files are kept on a separate single drive that gets triple backup love.
I want to switch from backing up my porn (lets call it data ;-) ) on DVD to saving my data on HDs (since cost/gig arn't that far appart anymore and bue-ray will IMHO not catch up fast enough in regards of cost/gig to be a good alternative for me).
But since loosing 1 HD (which can always happen) puts one back a couple of 100gigs at once I want some redundance.
Going for RAID 5 (I'm not willing to spend the extra money on RAID 6) has the huge disatvantage (for _my_ scenario) that if I loose 2 HDs (which also might happen since I plan to store the discs "offline" most of the time) _all_ my data is gone.
So I'm looking for a solution which stores my data in a "normal" way on the discs + one extra disk with the parity (somewhat like RAID 3 but without the striping).
I don't care about read/write speed too much, I just want the redundance and the cost effectiveness of RAID 5 (RAID 1 would also be too expensive for me) but without the danger of loosing all if more than 1 disc is gone*. Also, if I just want to read some data this way it should be sufficent to plug in just one disc instead of the whole array with RAID 5.
So, does anyone know if such a Sollution is allready implemented somewhere? (it also should be able to calculate the parity "on the fly" so that if I change one single file on one of the discs I don't have to wait until the parity of the whole array is recalculated but just for the corresponding sectors that have actually changed)
* this solution isn't that much better than RAID 5 with small arrays, but the more discs there are in the array, the more data will survive if 2 (or even more) discs die - with RAID 5 all is lost (and going for multiple 3 disc RAID 5 arrays isn't verry cost effective)
> So I'm looking for a solution which stores my data in a "normal" way on the discs + one extra disk with the parity (somewhat like RAID 3 but without the striping).
1. it does NOT join your drives together into one volume, each drive is separate (this is basically necessary for what you want unless you go the WHS route)
2. it has to be run on a dedicated system that it turns into NAS (you can't run it on your main desktop for instance)
that said, i really like the idea, almost all of the advantages of the WHS mechanism but much more space efficient (in most cases, i assume the largest drive will always be 'lost' to parity data)
Really, you're looking for something that is several RAID 1 mirrors of single volumes.
I can think of nothing off-the-shelf that fits all those needs, though "rolling your own" may help:
- Buy two drives. Create one large partition (say, D:) on drive 1. Mirror that.
- Buy two more drives. Create another large partition (say, E:) on drive 3. mirror that.
Etc, etc.
It's still the same volume, but if you do it using software, the two drives won't be dependent on each other in any way.
If you tear one of those drives out of your computer and slap it onto another one (USB connector, etc), then it'll come up just fine, with or without the mirror.
It's inelegant, and really not something I'd ever push on someone - but you've come up with a kind of oddball request, there. :) Might I ask what it's for? Maybe your criteria can be adjusted in some way.
> but you've come up with a kind of oddball request, there. :) Might I ask what it's for? Maybe your criteria can be adjusted in some way.
i understand what he's getting at
he wants protection from drive failure, so a 'parity drive' that can rebuild any one drive that fails is handy
but he's also concerned about losing more than 1 drive simultaneously
having just a plain filesystem on the disk is far more robust than any sort of striping system as worst comes to worst you can just yank any surviving drives and recover what's on them
- a series of raid 1 arrays (like what you described) works but isn't particularly flexible (need equal sized drives)
- WHS is more flexible and powerful but it still requires double the amount of storage (EXPENSIVE)
- this only requires 1 extra drive and allows it to backup any number of other drives
it comes from a desire for some protection but not being able or willing to spend enough for true duplication plus wanting something that fails gracefully (ie not raid5)
i would actually like something like that for my system, there's a chance of recovering everything, but if it hits the fan i'll be able to at least recover something plus it's not that expensive
don't forget there may be physical limitations. if you have 4 physical drives filled with data, you might have enough room and power connectors for a 5th drive, but not for 4 more
quote: 1. it does NOT join your drives together into one volume, each drive is separate (this is basically necessary for what you want unless you go the WHS route)
since unraid uses slackware there should be (at least in theory) a possibility to do this with the linux "Logical Volume Manager" (allthough one would probably have to do some work so that the TOC is saved on every disc to still being able to access the data if some of the other discs are gone)
But even without, seperate volumes and the option to access them one by one, by mounting the ReiserFS, is good enough for me.
quote: 2. it has to be run on a dedicated system that it turns into NAS (you can't run it on your main desktop for instance)
and that's a big downside.
When I have some time I'll probably try to run it in a virtual machine (the "use a physical disc" option in VM should reduce the perfomance-penaltys significantly), but I'm not that optimistic that this will also work with the "bigger", non-free Versions that can handle more than 3 discs (e.g. handling of the registration Key, since I allready ran into some pre-boot USB Issues with VM when I tried to test the bitlocker-feature of Vista in a VM - although it just might have been my old stick or my USB-contoller ..)
quote: i assume the largest drive will always be 'lost' to parity data)
yes (that's kind of a given) - the option to use discs of different sizes is a nice bonus though, since the array can now grow more "organically" over time (you just buy the disc with the best cost/gig ratio at the moment you need it without limmiting yourself to one size like with RAID 5)
quote: don't forget there may be physical limitations. if you have 4 physical drives filled with data, you might have enough room and power connectors for a 5th drive, but not for 4 more
with the port-multiplier Option of SATA II (up to 15 drives per cable) and an external casing I think there are ways to cope (and if you plan in advance to have X bays/connectors avalable, you just have to start a new array if the old one is full - which might be a good idea anyway as soon as you come close to double digit disc-numbers - although, that might take some time with modern disc sizes ;-) )
Again: I don't want nessecarily to being able to access my data all the time, I just want to switch from my current "DVD-storrage" to a "HD-storrage".
So what I'm looking for now is the funktionallity of unRAID (without the limitation of the drive nuber), being able to run in a VM and for free ;-).
I allready checked freeNAS and NASlite but they all seemed to be fixed either on RAID and/or JBOD without parity .. any suggestions?
> with the port-multiplier Option of SATA II (up to 15 drives per cable)
and which consumer level products support port-multipliers?
it's an optional part of the spec and most don't implement it
if you're willing to do a lot of extra work and hassle and really want offline storage you can fill a bunch of external drives with a virtual filesystem (like truecrypt for instance) and then with them all connected run par to build a par file across all your virtual disk files
disadvantages are numerous, have to be able to connect all disks at once, if you update one little piece of one drive have to recalculate the par file across all of them, etc
quote: and which consumer level products support port-multipliers?
most e-sata ports support it (although some controllers like the ones using JMB36X just support "Command-based Switching", e.g. all sollutions with Sil 3132 chips (e.g. many notebook S-ata - PCMCIA adapters) even support "FSI-based Switching" which works a little like SCSI (the command is sent to one disc and then the bus is free again, so you can get "close" to the theoretical 300 MB/sec with multiple discs and the bus is not blocked by one working disk (with 4 discs connected, a test showed still 40MB/sec transfer from each of the 4 parallel working discs ..)
so take AFAIKR one of the many new gigabyte mo-boards with 2 ports that can be used as e-sata, put e.g. a "Dawicontrol DC-6510 PM" on the other end of the cable (one is about 100 bucks) add a powersupply and a housing and you are good for 10 extra discs ..
quote: it's an optional part of the spec and most don't implement it
look at more recent motherboards (e-sata slowly shows up on more and more boards) and you'll find that it's supported more and more
quote: if you're willing to do a lot of extra work and hassle and really want offline storage you can fill a bunch of external drives with a virtual filesystem (like truecrypt for instance) and then with them all connected run par to build a par file across all your virtual disk files
well, I'm kind of too lazy to to the par thing each and every time I just change one little file - or to be more practical, I can verry much immagine myself pushing the rebuild further and further into the future as long as I can forsee that I will add more stuff in the verry near future which then again will require a rebuild .. (if I don't find a usable sollution which does it "on the fly" I'll probably end up doing it "by hand" (evetually by adding a small RAID 5 "file-buffer" to my System to strech the write/par Intervalls) but I _really_ would prefer an automatic solution without a most likely multi-hour rebuild process (reading all discs, calculating and writing the hole par-disk) after each little change ..)
Something I don't usually see in articles on Raid is the complete lack of protection from failure due to a virus or installation of a bad driver. Both disks get corrupted.
I am a home user of Raid 1 through a controller built in to the motherboard using a popular Redmond Washington operating system.
Yep - I touched briefly on this in the last part of the article.
Users need to look closely at if an ARCHIVAL system (tape, etc) is better for their needs than RAID 1.
Let's face it - RAID 1 is for "(almost) always on / critically needed to be working when powered up" configurations ONLY. How many home computers fall into this category... really?
Simply: It's a peice of data that the RAID controller can use to calculate the value of either of the other pieces of data in the chunk in the event of a disk failure.
Example: You have a three disk RAID 5 array. A file gets written in two pieces. Piece A gets written to disk one. Piece B gets written to disk two. The parity between the two is then generated and written to disk three. If disk one dies, the RAID controller can use Piece B and the parity data to generate what would have been Piece A. If disk two dies, the controller can generate Piece B. If disk three dies, the controller still has the original pieces of data. Thus, any single disk can fail before any data loss can occur.
RAID 5 is what is known as a distributed parity system, so the disk that holds parity alternated with each write. If a second file is written in the above example, disk one would get Piece A, disk two would get the parity, and disk three would get Piece B. This ensures that regardless of which disk dies, you always have two of the three pieces of data, which is all you need to get the original.
The reason RAID-5 uses distributed parity is to balance the disk accesses.
Most RAID-5 controllers do not read the parity data except during verification operations or when the array is degraded.
By rotating the parity blocks between disks 1-3, read operations can use all three disks instead of having a parity-only disk which is ignored by all reads.
I understand how the fault tolerance in the best case is half the drives in the 1+0 scenario, but that's still not worse than the RAID 5 scenario where you can't lose more than 1 drive no matter what.
So why was RAID 5 given a "Good" description while RAID 10/01 given a "Minimal" description?
RAID 0+1 (also known as a mirror of stripes) turns into a straight RAID 0 after one disk dies. The only way it will support a two disk failure is if disks on the same leg of the mirror die. If one on each side dies, you lose everything. After one disk failure, you lose all remaining fault tolerance. RAID 10 (or a stripe of mirrors) will sustain two disk failures if the disks are on different legs of the array. If it loses both disks on a single leg, you lose everything. Thus, it is far more likely that you'll lose the wrong two disks.
In a RAID 5 array, any single disk can be lost and you'll not lose anything--its position is irrelevant. Not only that, but a RAID 5 has better disk-to-storage efficiency (nx-1) when compared to RAID 0+1 and RAID 10 (nx/2). It's also less expensive to implement.
Overall, RAID 5 is one of the best fault tolerant features you can put into a system. RAID 6 is better, but it is also much more expensive.
Yes apparently to some people. Also one of the big bonus to Raid 0+1 is that you lose a drive and you do not suffer any performance degradation unlike RAID5 which until the RAID is rebuilt after a drive failure you take a big performance hit. If you are running a Exchange Cluster you cannot afford to take this performance hit during the middle of a busy work day unless you really do not like your helpdesk people. I think the one argument you could make is that a RAID 0+1 has more drives in a array to offer the same amount of storage as a RAID 5 volume so maybe you could make the statistical argument that the RAID 0+1 could be less fault tolerant. However to me this seems very tenuous.
You are, however, taking things a little out of context. Take a 6 drive configuration, for example. If you do a RAID 5 with four drives and two hotspares, you'll end up with the same usable capacity as a 6 disk RAID 0+1 - but with the "ability" to lose 3 drives.
Your comment about rebuilding is, however, completely backwards. You spend FAR more time rebuilding the mirrored set of a RAID 0+1 after a failed disk, because you need to rebuild the entire mirrored portion of array once again (since data has presumably changed, there's no parity, etc). (Don't believe me? Try it. ;)
Your general observation about being able to lose one disk in one or the other configuration is correct. You do need to compare apples-to-apples - a RAID 5 will offer you far more capacity if you build the same number of drives as in a 0+1, and a 0+1 will give you more performance. Apples-to-apples, though, you're going to get better redundancy OPTIONS out of the additional RAID 5 flexibility than you will with a 0+1.
Again, though, good points, and thanks again for reading.
What do you mean by hotspares? Do you mean a drive that you can swap in immediately after a drive fails? If that's the case, while in terms of economics it might be three "spares" in terms of actual data redundancy, it's still just one drive. If a drive fails while the spare is filling, you've still lost data.
In any case, it's quite clear that RAID will certainly give you more capacity, but the question was about the comment about data redundancy. I'll have to specify that it means to me how safe my data is in terms of absolute drive failures.
If you are using a SAN (Storage Area Network) were you might have say over 100+ disks were you build storage groups to assign to your servers that are connected into the SAN. This SAN will usually have various combinations of RAID 0,1,1_0,5. In this SAN you might have various types of disks says 300GB 10K FC and 146GB 15K FC Disks. You will keep a couple of these disks as hot spare. If say at 2AM the SAN detects in one of your RAID 1_0 Storage Groups that a disk has failed it will grab one of the hot spare disks and start re-building the RAID. The SAN will usually also send a alert of the various support teams that this has happened so the bad disk can be replaced. The SAN doesn't care where the hot spare is plugged into the SAN.
The biggest issue that I see as a ding against RAID 5 vs RAID 0+1 is the performance hit when a drive fails in a RAID 5. With a RAID 0+1 you suffer no performance hit when a drive fails because there is no parity rebuilding. With RAID 5 you can take a good performance hit until the RAID is rebuilt because of the parity calculation. Also with a SAN setup you can mirror a RAID 0+1 between physical DAE so the storage group will still stay up in the unlikely event of a complete DAE failure. Also even though in a RAID 0+1 you will have to rebuild the complete disk in the event of a drive failure with 15K RPM and 4GB FC backbone on the SAN this happens faster than you would think even when dealing with 500GB volumes. if you very concerned about losing another disk before the rebuild is complete you could use SnapView on your SAN to take a SnapShot of the disk and copy this data to your backup volume.
Personally we use Raid (0+1) at my work for our Exchange Cluster, SQL cluster and the home drives for our F&P cluster. Were Raid 0+1 is great is in a SAN environment. We have the drives mirror between SAN DAE so we could have a entire DAE fail on our SAN and for example Exchange will remain up and running. Also if you have a drive failure in one of our RAID 0+1 drives the SAN automatically just grabs the hot spare and starts rebuilding the array and pages the the lan team and alerts Dell to ship a new drive. Of course no matter what RAID you have setup you should always have daily tape backups with a copy of those tapes going offsite.
Might be asking a bit too much, especially in the case of RAID 5, 6, 0+1, and 1+0, but some SSD raid performance would be nice. They would need more than 2 drives wouldn't they?
However if we could see some RAID 0 figures from a pair off budget SSD's, and a pair of performance SSD's, that would be awesome.
1. software raid (like built into windows or linux)
2. motherboard raid solutions (nvraid and intel matrix)
3. low end products (highpoint and promise)
4. high end/enterprise products
5. more exotic raids like raid-z and raid 5ee
6. performance of mixing raids across same disks like you can with matrix raid and some adaptecs
and in addition to features/cost/performance i hope it really tries to test how reliable/bulletproof these solutions are
what happens if you yank the power in the middle of a write?
how easy is it to migrate an array to a different controller?
can disks in raid1 be yanked from the array and read directly or does it put header info on the disk that makes this impossible?
quote: for instance a ton of people have had problems with nvraid
That would be becasue "a ton of people are idiots'. I have been using nvRAID for a couple of years without issues, and most recently I even swapped motherboards, and the array was picked right up without a hitch once the proper BIOS settings were made. I would suspect that these people who are 'having problems' are the type who expect/believe that having a RAID0 array on their system will give them another 30 frames per second in the latest first person shooter as well . . .
> I would suspect that these people who are 'having problems' are the type who expect/believe that having a RAID0 array on their system will give them another 30 frames per second in the latest first person shooter as well . . .
the link is in the very top comment
they were all actually using raid1 and had problems with it constantly splitting the array
other features to consider:
handling dissimilar drives
morph online from one RAID level to another
easily add additional drives/capacity to an existing array
can you change which port a drive is connected to without messing up the array?
maybe create a big-honkin features matrix that shows which controllers are missing what?
performance:
- cpu hit between software raid, low-end controllers, enterprise controllers (some have reported high cpu usage with highpoint controllers even when using raid-1 which shouldn't cause much load)
- cpu hit with different busses (PCI, PCI-X, PCIe) and different connections (firewire, sata, scsi, sas, usb)
maybe even a corruption test. (write terabytes of data out under demanding situations and read back to ensure there was no corruption)
But most of all I WANT A TORTURE TEST. I want these arrays pushed to their limits and beyond. What does it take to make them fail? How gracefully do they handle it?
"Why? From our survey of a sample of our customers here's how it tends to happen:
The first and foremost risk is that the RAID BIOS loses the information it stores to track the allocation of the drives. We've seen this caused by all manner of software particularly anti-virus programs. Caught in time a simple recreation of the array (see last page) resolves the problem in over 90% of the cases.
BIOS changes, flashing the BIOS, resetting the BIOS, updating firmware etc can cause an array to fail. BIOS changes happen not just by hitting delete to enter setup. Software can make changes to the BIOS.
Disk managers, hard disk utilities, imaging and partitioning software etc. can often confuse a RAID array."
. . . . the probability of seeing two drives in the cluster fail within one hour is four times larger under the real data . . . .
Translation: one array drive failure means a much higher likelihood of another drive failure. The longer since the last failure, the longer to the next failure. Magic!
(perhaps intentionally mixing the manufacturers of drives in a raid is a good idea?)
> Someone claims that the nv sata controler (or maybe raid controler) doesn't work properly with the NCQ function of new hard drives (or the tagged queing or whatever WD calls it).
> if the drives are SATA II drives with 3 G/bps speed and NCQ features NVRAID Controller has know problems with this drives.
> the first test trying to copy data from the raid to the external firewire drive resulted in not 1 but 2 drives dropping out.
Luckily the 2 were both 1 half of the mirror meaning i could rebuild the raid. So looks like trying to use the firewire from the raid is the problem. THis may stand to reason as the firewire card is via an add-on card in a PCI slot so maybe there is some weird bottleneck in the bus when doing this causing the nvraid to malfunction.
> I have read that its best to disable ncq and also read cache from all drives in the raid via the device manager. This may tie in with someone else’s post here who says the nvraid has issues with ncq drives.
Good posts. A topic you're obviously interested in. :)
Let me try and hit a few of the points in random order:
- Stress/break testing is a GOOD idea, but very highly subjective. You can't GUARANTEE that you'll be writing (or reading) EXACTLY the same data under EXACTLY the same circumstances, so there's always that element of uncertainty. Even opening the same file can't guarantee that the same segments are on the same disk, so... I'll have to give some thought to that. Definitely worthwhile, though, to pursue that angle (especially in terms of looking at how array controllers recover from major issues like that).
- Your other points pretty much all hit on a major argument: Software versus Hardware RAID (and versus proprietary hardware). I actually know an IT Director in a major (Fortune 500) company who uses software RAID exclusively, including in fairly intensive I/O applications. His argument? "I've been burned by "good" hardware too often - it lasts 7 years, I forget to replace it, and when the controller cooks, my array is done." (Make whatever argument you like about him not being on the ball enough to replace his 7 year old equipment, but I digress). I do find the majority of the decent controllers write header information in fairly documented (and retrievable) ways - look at IBM's SmartRAID series as a random example of this - so I don't see that being a hugely big deal anymore.
You're dead on, though. *CONSUMERS* who are looking at RAID need to be very, very sure they know what they're getting themselves into.
> You can't GUARANTEE that you'll be writing (or reading) EXACTLY the same data under EXACTLY the same circumstances, so there's always that element of uncertainty
that's true, but i don't think it's that important
have a test where you're copying a thousand small files and yank the power in the middle
run this test 5-10 times and see how they compare
controller 1 never has a problem
controller 2 required a complete rebuild 5 times
maybe you can't exactly duplicate the circumstances, but it's enough to say controller 2 has problems
(actually requiring a complete rebuild even once would be a serious problem)
similarly, have a heavy read/write pattern with random data while simultaneously writing data out a pci firewire card and maybe even a usb drive and have audio playing and high network traffic (as much bus traffic and conflict as you can generate) that runs for 6 hours
controller 1 has 0 bit errors in that 6 hours
controller 2 has 200 bit errors in that 6 hours
controller 2 obviously has problems even if you can't exactly duplicate it
i think it's sufficient to merely show that a controller could corrupt your data
The biggest issue with RAID are the unrecoverable read errors. If you loose the drive, the RAID has to read 100% of the remaining drives even if there is no data on portions of the drive. If you get an error on rebuild, the entire array will die.
A UER on SATA of 1 in 10^14 bits read means a read failure every 12.5 terabytes. A 500 GB drive has 0.04E14 bits, so in the worst case rebuilding that drive in a five-drive RAID-5 group means transferring 0.20E14 bits. This means there is a 20% probability of an unrecoverable error during the rebuild. Enterprise class disks are less prone to this problem:
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ShadowFlash - Monday, March 2, 2009 - link
RAID 10 not as fault tolerant as RAID 5 ??? unlikely...RAID 5 is used when capacity cannot be sacrificed for the increased data protection of RAID 10. Yes, RAID 0+1 is horrible, and should be avoided as mentioned in other posts. RAID 10 sets will absolutely rebuild faster than a RAID 5 in almost all situations. With the dirt cheap pricing of modern large capacity drives, I can think of almost no situation where RAID 5 is preferable to RAID 10. The flaw is in the way hard drives die, and parity. I was going to type out a long explanation, but this link covers it well.http://miracleas.com/BAARF/RAID5_versus_RAID10.txt">http://miracleas.com/BAARF/RAID5_versus_RAID10.txt
I strongly urge any home user not to use RAID 5 ( or any other parity form of RAID ). RAID 5 is antiquated and left over from the days when cost vs capacity was a major concern. RAID 10 also dosen't require as expensive of a controller card.
And remember if you do insist on RAID 5 to never use it as a system disk. The parity overhead from the many small writes an OS performs is far too great a penalty.
I'm not trying to start a fight, just trying to educate on the flaws of parity.
Codesmith - Sunday, September 9, 2007 - link
The drives in my 2 drive RAID 1 array are 100% readable as normal drives by any SATA controller.With any other RAID configuration you are dependent on both remembering the proper settings, performing the rebuild properly and most importantly, finding a compatible controller.
Until the manufactures decide to standardize, the system you have in place to protect your data could have you waiting days to access your data.
I am planning to add a RAID 5/6 array for home theater usage, but the business documents are staying on the RAID 1 array.
Anonymous Freak - Saturday, September 8, 2007 - link
That's my acronym for it. It also describes my desire for it.RAID = Redundant Array of Independent Disks.
AIDS = Array of Independent Disks, Striped.
"RAID" 0 has very few legitimate uses. If you value the data stored at all, and have any care at all about uptime, it's inappropriate. If all you want is an ultra-fast 'scratch' disk, it is appropriate. Before ultra-large drives, I used a RAID-0 of 9 GB, 10k RPM SCSI drives as my capture and edit partition for video editing, and that's about it. Once the editing was done, I wrote the finished file back out to DV tape, and transcoded to something more manageable for computer use, and storage on my main ATA hard drive.
MadAd - Saturday, September 8, 2007 - link
[quote]"Higher quality RAID 1 controllers can outperform single drive implementations by making both drives active for read operations. This can in theory reduce file access times (requests are sent to whichever drive is closer to the desired data) as well as potentially doubling data throughput on reads"[/quote]Its not the best place to post here I know, but as a home user with a 1tb 0+1 pata array on a promise fastrack (on a budget) I was thinking of looking on ebay for a reliable replacement controller with the above characteristics, but dont know what series cards are both inexpensive for a second user now and fit an x32 pci.
Thanks a lot
tynopik - Saturday, September 8, 2007 - link
> but as a home user with a 1tb 0+1 pata array on a promise fastrack (on a budget) I was thinking of looking on ebay for a reliable replacement controller with the above characteristics, but dont know what series cards are both inexpensive for a second user now and fit an x32 pci.saying you currently have a 0+1 array i assume you have at least 4 drives, probably 4 500gb drives
since 0+1 provides the speed of raid0 with the mirroring of raid1 i'm not sure what you're looking for. if you went for a straight raid1 solution your system would see 2 500gb volumes instead of 1 1tb volume.
and not sure what you mean by x32 pci, just a regular pci slot? if you're talking about PCIe they only go to x16 and can't say i'm aware of any 'reasonable' card that uses more than x8
MadAd - Sunday, September 9, 2007 - link
urm....no4x250 and im wondering what enterprise class controller is cheap on ebay that uses pata drives, an x32 pci slot
(not pcie, see- http://en.wikipedia.org/wiki/Peripheral_Component_...">http://en.wikipedia.org/wiki/Peripheral_Component_...
and performs as quoted from the article, because my promise controller is good but still a home class controller. Just i dont know the enterprise segment at all and I thought some of these guys would.
tynopik - Sunday, September 9, 2007 - link
> 4x250then you aren't using raid0+1, just raid0
> (not pcie, see- http://en.wikipedia.org/wiki/Peripheral_Component_...">http://en.wikipedia.org/wiki/Peripheral_Component_...
it's the x32 that is confusing
if you search that page you will see x32 doesn't show up anywhere on it
i'm going to assume you just mean 32-bit PCI which is standard which is what practically every motherboard manufactured today has at least one of
but still i can't answer your question about which PCI (no need to say 32-bit, it's assumed) raid controllers support IDE drives with enhanced read speed, sorry
MadAd - Sunday, September 9, 2007 - link
http://en.wikipedia.org/wiki/Peripheral_Component_...">http://en.wikipedia.org/wiki/Peripheral_Component_...Zak - Saturday, September 8, 2007 - link
I gave up on RAID "for protection" a long time ago. I tried everything from software RAID to on-board 1 and 5, and to $300 cards with controllers and on-board RAM and 5 hard drives. It is not worth the hassle for home use or even small business, period. I absolutely agree with that article from Pudget computers. I had more problems due to raid controllers acting up than hard drive failures. RAID will nor protect you against directory corruption, accidental deletion and infections - things that happen A LOT more often than hard drive failures. RAID adds level of complexity that involves extra maintenance and extra cost.My current solution is two external FW or USB drivers. I run two redundant Retrospect backups every 12 hours, one right after another that backs up my storage drive plus one at night that mirrors the drive to another. It's probably an overkill but I'll take it over any RAID5 any time: three separate drives, three separate file systems - total protection against file deletion, directory corruption and infections (the external drives are dismounted between backups. I do the same on Macs and PCs.
I still may use RAID0 for scratch and system disks for speed, but my files are kept on a separate single drive that gets triple backup love.
Zak
Sudder - Saturday, September 8, 2007 - link
Hi,can anybody point me in the right direction?
I want to switch from backing up my porn (lets call it data ;-) ) on DVD to saving my data on HDs (since cost/gig arn't that far appart anymore and bue-ray will IMHO not catch up fast enough in regards of cost/gig to be a good alternative for me).
But since loosing 1 HD (which can always happen) puts one back a couple of 100gigs at once I want some redundance.
Going for RAID 5 (I'm not willing to spend the extra money on RAID 6) has the huge disatvantage (for _my_ scenario) that if I loose 2 HDs (which also might happen since I plan to store the discs "offline" most of the time) _all_ my data is gone.
So I'm looking for a solution which stores my data in a "normal" way on the discs + one extra disk with the parity (somewhat like RAID 3 but without the striping).
I don't care about read/write speed too much, I just want the redundance and the cost effectiveness of RAID 5 (RAID 1 would also be too expensive for me) but without the danger of loosing all if more than 1 disc is gone*. Also, if I just want to read some data this way it should be sufficent to plug in just one disc instead of the whole array with RAID 5.
So, does anyone know if such a Sollution is allready implemented somewhere? (it also should be able to calculate the parity "on the fly" so that if I change one single file on one of the discs I don't have to wait until the parity of the whole array is recalculated but just for the corresponding sectors that have actually changed)
* this solution isn't that much better than RAID 5 with small arrays, but the more discs there are in the array, the more data will survive if 2 (or even more) discs die - with RAID 5 all is lost (and going for multiple 3 disc RAID 5 arrays isn't verry cost effective)
tynopik - Saturday, September 8, 2007 - link
> So I'm looking for a solution which stores my data in a "normal" way on the discs + one extra disk with the parity (somewhat like RAID 3 but without the striping).unRAID
http://www.lime-technology.com/">http://www.lime-technology.com/
tynopik - Saturday, September 8, 2007 - link
i should point out that1. it does NOT join your drives together into one volume, each drive is separate (this is basically necessary for what you want unless you go the WHS route)
2. it has to be run on a dedicated system that it turns into NAS (you can't run it on your main desktop for instance)
that said, i really like the idea, almost all of the advantages of the WHS mechanism but much more space efficient (in most cases, i assume the largest drive will always be 'lost' to parity data)
Dave Robinet - Saturday, September 8, 2007 - link
Really, you're looking for something that is several RAID 1 mirrors of single volumes.I can think of nothing off-the-shelf that fits all those needs, though "rolling your own" may help:
- Buy two drives. Create one large partition (say, D:) on drive 1. Mirror that.
- Buy two more drives. Create another large partition (say, E:) on drive 3. mirror that.
Etc, etc.
It's still the same volume, but if you do it using software, the two drives won't be dependent on each other in any way.
If you tear one of those drives out of your computer and slap it onto another one (USB connector, etc), then it'll come up just fine, with or without the mirror.
It's inelegant, and really not something I'd ever push on someone - but you've come up with a kind of oddball request, there. :) Might I ask what it's for? Maybe your criteria can be adjusted in some way.
tynopik - Saturday, September 8, 2007 - link
> but you've come up with a kind of oddball request, there. :) Might I ask what it's for? Maybe your criteria can be adjusted in some way.i understand what he's getting at
he wants protection from drive failure, so a 'parity drive' that can rebuild any one drive that fails is handy
but he's also concerned about losing more than 1 drive simultaneously
having just a plain filesystem on the disk is far more robust than any sort of striping system as worst comes to worst you can just yank any surviving drives and recover what's on them
- a series of raid 1 arrays (like what you described) works but isn't particularly flexible (need equal sized drives)
- WHS is more flexible and powerful but it still requires double the amount of storage (EXPENSIVE)
- this only requires 1 extra drive and allows it to backup any number of other drives
it comes from a desire for some protection but not being able or willing to spend enough for true duplication plus wanting something that fails gracefully (ie not raid5)
i would actually like something like that for my system, there's a chance of recovering everything, but if it hits the fan i'll be able to at least recover something plus it's not that expensive
don't forget there may be physical limitations. if you have 4 physical drives filled with data, you might have enough room and power connectors for a 5th drive, but not for 4 more
Sudder - Sunday, September 9, 2007 - link
tnx, this goes a big step in the right direction
since unraid uses slackware there should be (at least in theory) a possibility to do this with the linux "Logical Volume Manager" (allthough one would probably have to do some work so that the TOC is saved on every disc to still being able to access the data if some of the other discs are gone)
But even without, seperate volumes and the option to access them one by one, by mounting the ReiserFS, is good enough for me.
and that's a big downside.
When I have some time I'll probably try to run it in a virtual machine (the "use a physical disc" option in VM should reduce the perfomance-penaltys significantly), but I'm not that optimistic that this will also work with the "bigger", non-free Versions that can handle more than 3 discs (e.g. handling of the registration Key, since I allready ran into some pre-boot USB Issues with VM when I tried to test the bitlocker-feature of Vista in a VM - although it just might have been my old stick or my USB-contoller ..)
yes (that's kind of a given) - the option to use discs of different sizes is a nice bonus though, since the array can now grow more "organically" over time (you just buy the disc with the best cost/gig ratio at the moment you need it without limmiting yourself to one size like with RAID 5)
with the port-multiplier Option of SATA II (up to 15 drives per cable) and an external casing I think there are ways to cope (and if you plan in advance to have X bays/connectors avalable, you just have to start a new array if the old one is full - which might be a good idea anyway as soon as you come close to double digit disc-numbers - although, that might take some time with modern disc sizes ;-) )
Again: I don't want nessecarily to being able to access my data all the time, I just want to switch from my current "DVD-storrage" to a "HD-storrage".
So what I'm looking for now is the funktionallity of unRAID (without the limitation of the drive nuber), being able to run in a VM and for free ;-).
I allready checked freeNAS and NASlite but they all seemed to be fixed either on RAID and/or JBOD without parity .. any suggestions?
tynopik - Sunday, September 9, 2007 - link
> with the port-multiplier Option of SATA II (up to 15 drives per cable)and which consumer level products support port-multipliers?
it's an optional part of the spec and most don't implement it
if you're willing to do a lot of extra work and hassle and really want offline storage you can fill a bunch of external drives with a virtual filesystem (like truecrypt for instance) and then with them all connected run par to build a par file across all your virtual disk files
disadvantages are numerous, have to be able to connect all disks at once, if you update one little piece of one drive have to recalculate the par file across all of them, etc
Sudder - Sunday, September 9, 2007 - link
most e-sata ports support it (although some controllers like the ones using JMB36X just support "Command-based Switching", e.g. all sollutions with Sil 3132 chips (e.g. many notebook S-ata - PCMCIA adapters) even support "FSI-based Switching" which works a little like SCSI (the command is sent to one disc and then the bus is free again, so you can get "close" to the theoretical 300 MB/sec with multiple discs and the bus is not blocked by one working disk (with 4 discs connected, a test showed still 40MB/sec transfer from each of the 4 parallel working discs ..)
so take AFAIKR one of the many new gigabyte mo-boards with 2 ports that can be used as e-sata, put e.g. a "Dawicontrol DC-6510 PM" on the other end of the cable (one is about 100 bucks) add a powersupply and a housing and you are good for 10 extra discs ..
look at more recent motherboards (e-sata slowly shows up on more and more boards) and you'll find that it's supported more and more
well, I'm kind of too lazy to to the par thing each and every time I just change one little file - or to be more practical, I can verry much immagine myself pushing the rebuild further and further into the future as long as I can forsee that I will add more stuff in the verry near future which then again will require a rebuild .. (if I don't find a usable sollution which does it "on the fly" I'll probably end up doing it "by hand" (evetually by adding a small RAID 5 "file-buffer" to my System to strech the write/par Intervalls) but I _really_ would prefer an automatic solution without a most likely multi-hour rebuild process (reading all discs, calculating and writing the hole par-disk) after each little change ..)
Witling - Saturday, September 8, 2007 - link
Something I don't usually see in articles on Raid is the complete lack of protection from failure due to a virus or installation of a bad driver. Both disks get corrupted.I am a home user of Raid 1 through a controller built in to the motherboard using a popular Redmond Washington operating system.
Dave Robinet - Saturday, September 8, 2007 - link
Yep - I touched briefly on this in the last part of the article.Users need to look closely at if an ARCHIVAL system (tape, etc) is better for their needs than RAID 1.
Let's face it - RAID 1 is for "(almost) always on / critically needed to be working when powered up" configurations ONLY. How many home computers fall into this category... really?
kobymu - Saturday, September 8, 2007 - link
In certain cases RAID 1 will give you better read performance.
munim - Friday, September 7, 2007 - link
I don't understand what the parity portion is in RAID 5, anyone care to explain?drebo - Friday, September 7, 2007 - link
Simply: It's a peice of data that the RAID controller can use to calculate the value of either of the other pieces of data in the chunk in the event of a disk failure.Example: You have a three disk RAID 5 array. A file gets written in two pieces. Piece A gets written to disk one. Piece B gets written to disk two. The parity between the two is then generated and written to disk three. If disk one dies, the RAID controller can use Piece B and the parity data to generate what would have been Piece A. If disk two dies, the controller can generate Piece B. If disk three dies, the controller still has the original pieces of data. Thus, any single disk can fail before any data loss can occur.
RAID 5 is what is known as a distributed parity system, so the disk that holds parity alternated with each write. If a second file is written in the above example, disk one would get Piece A, disk two would get the parity, and disk three would get Piece B. This ensures that regardless of which disk dies, you always have two of the three pieces of data, which is all you need to get the original.
Zan Lynx - Tuesday, September 11, 2007 - link
The reason RAID-5 uses distributed parity is to balance the disk accesses.Most RAID-5 controllers do not read the parity data except during verification operations or when the array is degraded.
By rotating the parity blocks between disks 1-3, read operations can use all three disks instead of having a parity-only disk which is ignored by all reads.
ChronoReverse - Friday, September 7, 2007 - link
I understand how the fault tolerance in the best case is half the drives in the 1+0 scenario, but that's still not worse than the RAID 5 scenario where you can't lose more than 1 drive no matter what.So why was RAID 5 given a "Good" description while RAID 10/01 given a "Minimal" description?
drebo - Friday, September 7, 2007 - link
RAID 0+1 (also known as a mirror of stripes) turns into a straight RAID 0 after one disk dies. The only way it will support a two disk failure is if disks on the same leg of the mirror die. If one on each side dies, you lose everything. After one disk failure, you lose all remaining fault tolerance. RAID 10 (or a stripe of mirrors) will sustain two disk failures if the disks are on different legs of the array. If it loses both disks on a single leg, you lose everything. Thus, it is far more likely that you'll lose the wrong two disks.In a RAID 5 array, any single disk can be lost and you'll not lose anything--its position is irrelevant. Not only that, but a RAID 5 has better disk-to-storage efficiency (nx-1) when compared to RAID 0+1 and RAID 10 (nx/2). It's also less expensive to implement.
Overall, RAID 5 is one of the best fault tolerant features you can put into a system. RAID 6 is better, but it is also much more expensive.
ChronoReverse - Saturday, September 8, 2007 - link
So in RAID 5 you can lose any ONE drive.In RAID 1+0/0+1, you can also lose any ONE drive.
In RAID 5 you CANNOT lose a second drive.
In RAID 1+0/0+1, there's a CHANCE you might survive a second drive failure.
Therefore, RAID 5 is more fault-tolerant.
Brovane - Saturday, September 8, 2007 - link
Yes apparently to some people. Also one of the big bonus to Raid 0+1 is that you lose a drive and you do not suffer any performance degradation unlike RAID5 which until the RAID is rebuilt after a drive failure you take a big performance hit. If you are running a Exchange Cluster you cannot afford to take this performance hit during the middle of a busy work day unless you really do not like your helpdesk people. I think the one argument you could make is that a RAID 0+1 has more drives in a array to offer the same amount of storage as a RAID 5 volume so maybe you could make the statistical argument that the RAID 0+1 could be less fault tolerant. However to me this seems very tenuous.Dave Robinet - Saturday, September 8, 2007 - link
Good comments, and thanks for reading.You are, however, taking things a little out of context. Take a 6 drive configuration, for example. If you do a RAID 5 with four drives and two hotspares, you'll end up with the same usable capacity as a 6 disk RAID 0+1 - but with the "ability" to lose 3 drives.
Your comment about rebuilding is, however, completely backwards. You spend FAR more time rebuilding the mirrored set of a RAID 0+1 after a failed disk, because you need to rebuild the entire mirrored portion of array once again (since data has presumably changed, there's no parity, etc). (Don't believe me? Try it. ;)
Your general observation about being able to lose one disk in one or the other configuration is correct. You do need to compare apples-to-apples - a RAID 5 will offer you far more capacity if you build the same number of drives as in a 0+1, and a 0+1 will give you more performance. Apples-to-apples, though, you're going to get better redundancy OPTIONS out of the additional RAID 5 flexibility than you will with a 0+1.
Again, though, good points, and thanks again for reading.
dave
ChronoReverse - Sunday, September 9, 2007 - link
What do you mean by hotspares? Do you mean a drive that you can swap in immediately after a drive fails? If that's the case, while in terms of economics it might be three "spares" in terms of actual data redundancy, it's still just one drive. If a drive fails while the spare is filling, you've still lost data.In any case, it's quite clear that RAID will certainly give you more capacity, but the question was about the comment about data redundancy. I'll have to specify that it means to me how safe my data is in terms of absolute drive failures.
Brovane - Monday, September 10, 2007 - link
If you are using a SAN (Storage Area Network) were you might have say over 100+ disks were you build storage groups to assign to your servers that are connected into the SAN. This SAN will usually have various combinations of RAID 0,1,1_0,5. In this SAN you might have various types of disks says 300GB 10K FC and 146GB 15K FC Disks. You will keep a couple of these disks as hot spare. If say at 2AM the SAN detects in one of your RAID 1_0 Storage Groups that a disk has failed it will grab one of the hot spare disks and start re-building the RAID. The SAN will usually also send a alert of the various support teams that this has happened so the bad disk can be replaced. The SAN doesn't care where the hot spare is plugged into the SAN.The biggest issue that I see as a ding against RAID 5 vs RAID 0+1 is the performance hit when a drive fails in a RAID 5. With a RAID 0+1 you suffer no performance hit when a drive fails because there is no parity rebuilding. With RAID 5 you can take a good performance hit until the RAID is rebuilt because of the parity calculation. Also with a SAN setup you can mirror a RAID 0+1 between physical DAE so the storage group will still stay up in the unlikely event of a complete DAE failure. Also even though in a RAID 0+1 you will have to rebuild the complete disk in the event of a drive failure with 15K RPM and 4GB FC backbone on the SAN this happens faster than you would think even when dealing with 500GB volumes. if you very concerned about losing another disk before the rebuild is complete you could use SnapView on your SAN to take a SnapShot of the disk and copy this data to your backup volume.
Brovane - Friday, September 7, 2007 - link
Personally we use Raid (0+1) at my work for our Exchange Cluster, SQL cluster and the home drives for our F&P cluster. Were Raid 0+1 is great is in a SAN environment. We have the drives mirror between SAN DAE so we could have a entire DAE fail on our SAN and for example Exchange will remain up and running. Also if you have a drive failure in one of our RAID 0+1 drives the SAN automatically just grabs the hot spare and starts rebuilding the array and pages the the lan team and alerts Dell to ship a new drive. Of course no matter what RAID you have setup you should always have daily tape backups with a copy of those tapes going offsite.Bladen - Friday, September 7, 2007 - link
Might be asking a bit too much, especially in the case of RAID 5, 6, 0+1, and 1+0, but some SSD raid performance would be nice. They would need more than 2 drives wouldn't they?However if we could see some RAID 0 figures from a pair off budget SSD's, and a pair of performance SSD's, that would be awesome.
tynopik - Friday, September 7, 2007 - link
in addition to a WHS comparison i hope it covers1. software raid (like built into windows or linux)
2. motherboard raid solutions (nvraid and intel matrix)
3. low end products (highpoint and promise)
4. high end/enterprise products
5. more exotic raids like raid-z and raid 5ee
6. performance of mixing raids across same disks like you can with matrix raid and some adaptecs
and in addition to features/cost/performance i hope it really tries to test how reliable/bulletproof these solutions are
for instance a ton of people have had problems with nvraid
http://www.nforcershq.com/forum/image-vp511756.htm...">http://www.nforcershq.com/forum/image-vp511756.htm...
what happens if you yank the power in the middle of a write?
how easy is it to migrate an array to a different controller?
can disks in raid1 be yanked from the array and read directly or does it put header info on the disk that makes this impossible?
yyrkoon - Saturday, September 8, 2007 - link
That would be becasue "a ton of people are idiots'. I have been using nvRAID for a couple of years without issues, and most recently I even swapped motherboards, and the array was picked right up without a hitch once the proper BIOS settings were made. I would suspect that these people who are 'having problems' are the type who expect/believe that having a RAID0 array on their system will give them another 30 frames per second in the latest first person shooter as well . . .
tynopik - Saturday, September 8, 2007 - link
> I would suspect that these people who are 'having problems' are the type who expect/believe that having a RAID0 array on their system will give them another 30 frames per second in the latest first person shooter as well . . .the link is in the very top comment
they were all actually using raid1 and had problems with it constantly splitting the array
tynopik - Friday, September 7, 2007 - link
http://storageadvisors.adaptec.com/">http://storageadvisors.adaptec.com/great site with lots of potential topics like:
desktop vs raid/enterprise drives - is there a difference
http://storageadvisors.adaptec.com/2006/11/20/desk...">http://storageadvisors.adaptec.com/2006...-drives-...
Picking the right stripe size
http://storageadvisors.adaptec.com/2006/06/05/pick...">http://storageadvisors.adaptec.com/2006/06/05/pick...
Different types of RAID6
http://storageadvisors.adaptec.com/2005/11/07/a-ta...">http://storageadvisors.adaptec.com/2005/11/07/a-ta...
other features to consider:
handling dissimilar drives
morph online from one RAID level to another
easily add additional drives/capacity to an existing array
can you change which port a drive is connected to without messing up the array?
maybe create a big-honkin features matrix that shows which controllers are missing what?
performance:
- cpu hit between software raid, low-end controllers, enterprise controllers (some have reported high cpu usage with highpoint controllers even when using raid-1 which shouldn't cause much load)
- cpu hit with different busses (PCI, PCI-X, PCIe) and different connections (firewire, sata, scsi, sas, usb)
maybe even a corruption test. (write terabytes of data out under demanding situations and read back to ensure there was no corruption)
But most of all I WANT A TORTURE TEST. I want these arrays pushed to their limits and beyond. What does it take to make them fail? How gracefully do they handle it?
tynopik - Friday, September 7, 2007 - link
an article from the anti-raid perspectivehttp://www.pugetsystems.com/articles?&id=29">http://www.pugetsystems.com/articles?&id=29
tynopik - Saturday, September 8, 2007 - link
another semi-anti-raid piecehttp://www.bestpricecomputers.co.uk/reviews/home-p...">http://www.bestpricecomputers.co.uk/reviews/home-p...
"Why? From our survey of a sample of our customers here's how it tends to happen:
The first and foremost risk is that the RAID BIOS loses the information it stores to track the allocation of the drives. We've seen this caused by all manner of software particularly anti-virus programs. Caught in time a simple recreation of the array (see last page) resolves the problem in over 90% of the cases.
BIOS changes, flashing the BIOS, resetting the BIOS, updating firmware etc can cause an array to fail. BIOS changes happen not just by hitting delete to enter setup. Software can make changes to the BIOS.
Disk managers, hard disk utilities, imaging and partitioning software etc. can often confuse a RAID array."
-------------------------
http://storagemojo.com/?p=383">http://storagemojo.com/?p=383
. . . . the probability of seeing two drives in the cluster fail within one hour is four times larger under the real data . . . .
Translation: one array drive failure means a much higher likelihood of another drive failure. The longer since the last failure, the longer to the next failure. Magic!
(perhaps intentionally mixing the manufacturers of drives in a raid is a good idea?)
------------------
http://www.lime-technology.com/">http://www.lime-technology.com/
unRAID
-----------------
http://www.miracleas.com/BAARF/">http://www.miracleas.com/BAARF/
an amusing little page
-----------------
it would also be cool if you had a failing drive that behaved erratically/intermittently/partially to test these systems
-----------------
if a drive fails in a raid array and you pull the wrong drive, can you stick it back in and still recover or does the controller wig out?
------------------
some parts from the thread at the top that you might have missed
http://www.nforcershq.com/forum/3-vt61937.html?pos...">http://www.nforcershq.com/forum/3-vt619...=0&p...
> Someone claims that the nv sata controler (or maybe raid controler) doesn't work properly with the NCQ function of new hard drives (or the tagged queing or whatever WD calls it).
> if the drives are SATA II drives with 3 G/bps speed and NCQ features NVRAID Controller has know problems with this drives.
> the first test trying to copy data from the raid to the external firewire drive resulted in not 1 but 2 drives dropping out.
Luckily the 2 were both 1 half of the mirror meaning i could rebuild the raid. So looks like trying to use the firewire from the raid is the problem. THis may stand to reason as the firewire card is via an add-on card in a PCI slot so maybe there is some weird bottleneck in the bus when doing this causing the nvraid to malfunction.
(so like check high pci bus competition)
http://www.nforcershq.com/forum/4-vt61937.html?sta...">http://www.nforcershq.com/forum/4-vt61937.html?sta...
> I have read that its best to disable ncq and also read cache from all drives in the raid via the device manager. This may tie in with someone else’s post here who says the nvraid has issues with ncq drives.
http://www.nforcershq.com/forum/image-vp591021.htm...">http://www.nforcershq.com/forum/image-vp591021.htm...
NF4 + Vista + RAID1 = no NCQ?
------------------------------------
RAID is dead, all hail the storage robot
http://www.daniweb.com/blogs/printentry1399.html">http://www.daniweb.com/blogs/printentry1399.html
Drobo - The World's first storage robot
http://www.datarobotics.com/">http://www.datarobotics.com/
"Drobo changes the way you think about storage. In short, it's the best solution for managing external storage needs I have used." - JupiterResearch
"It is the iPod of mass storage" - ZDNet
"...the most impressive multi-drive storage solution for PCs I've seen to date" - eHomeUpgrade
sucks that it's $500 without drives and usb only though
Dave Robinet - Saturday, September 8, 2007 - link
Good posts. A topic you're obviously interested in. :)Let me try and hit a few of the points in random order:
- Stress/break testing is a GOOD idea, but very highly subjective. You can't GUARANTEE that you'll be writing (or reading) EXACTLY the same data under EXACTLY the same circumstances, so there's always that element of uncertainty. Even opening the same file can't guarantee that the same segments are on the same disk, so... I'll have to give some thought to that. Definitely worthwhile, though, to pursue that angle (especially in terms of looking at how array controllers recover from major issues like that).
- Your other points pretty much all hit on a major argument: Software versus Hardware RAID (and versus proprietary hardware). I actually know an IT Director in a major (Fortune 500) company who uses software RAID exclusively, including in fairly intensive I/O applications. His argument? "I've been burned by "good" hardware too often - it lasts 7 years, I forget to replace it, and when the controller cooks, my array is done." (Make whatever argument you like about him not being on the ball enough to replace his 7 year old equipment, but I digress). I do find the majority of the decent controllers write header information in fairly documented (and retrievable) ways - look at IBM's SmartRAID series as a random example of this - so I don't see that being a hugely big deal anymore.
You're dead on, though. *CONSUMERS* who are looking at RAID need to be very, very sure they know what they're getting themselves into.
tynopik - Saturday, September 8, 2007 - link
> You can't GUARANTEE that you'll be writing (or reading) EXACTLY the same data under EXACTLY the same circumstances, so there's always that element of uncertaintythat's true, but i don't think it's that important
have a test where you're copying a thousand small files and yank the power in the middle
run this test 5-10 times and see how they compare
controller 1 never has a problem
controller 2 required a complete rebuild 5 times
maybe you can't exactly duplicate the circumstances, but it's enough to say controller 2 has problems
(actually requiring a complete rebuild even once would be a serious problem)
similarly, have a heavy read/write pattern with random data while simultaneously writing data out a pci firewire card and maybe even a usb drive and have audio playing and high network traffic (as much bus traffic and conflict as you can generate) that runs for 6 hours
controller 1 has 0 bit errors in that 6 hours
controller 2 has 200 bit errors in that 6 hours
controller 2 obviously has problems even if you can't exactly duplicate it
i think it's sufficient to merely show that a controller could corrupt your data
alecweder - Wednesday, February 4, 2015 - link
The biggest issue with RAID are the unrecoverable read errors.If you loose the drive, the RAID has to read 100% of the remaining drives even if there is no data on portions of the drive. If you get an error on rebuild, the entire array will die.
http://www.enterprisestorageforum.com/storage-mana...
A UER on SATA of 1 in 10^14 bits read means a read failure every 12.5 terabytes. A 500
GB drive has 0.04E14 bits, so in the worst case rebuilding that drive in a five-drive
RAID-5 group means transferring 0.20E14 bits. This means there is a 20% probability
of an unrecoverable error during the rebuild. Enterprise class disks are less prone to this problem:
http://www.lucidti.com/zfs-checksums-add-reliabili...