Not to sound like a broken record, but with the exception of OCZ's Vertex LE, not much has changed in the SSD market over the past couple of years. Intel still seems like the safest bet, and these days they're even offering a pretty compelling value.

The 80GB X25-M G2 is finally selling for reasonable prices and earlier this month Intel launched its first value SSD: the X25-V. Priced at $125, the X25-V gives you much of the performance of the X25-M but at a lower cost and capacity point. It's a great way to safely transition to an SSD.

Intel's X25-V uses the same controller as the X25-M G2, but with half the NAND and thus half the channels

For months now you all have been asking me to tackle the topic of RAIDing SSDs. I've been cautious about doing so for a number of reasons:

1) There is currently no way to pass the TRIM instruction to a drive that is a member of a RAID array. Intel's latest RAID drivers allow you to TRIM non-member RAID disks, but not an SSD in a RAID array.

2) Giving up TRIM support means that you need a fairly resilient SSD, one whose performance will not degrade tremendously over time. On the bright side, with the exception of the newer SandForce controllers, I'm not sure we've seen a controller as resilient as Intel's.

A couple of weeks ago I published some early results of Intel's X25-V SSD. But I was holding out on you, I actually had two:

Using the same Intel X58 testbed I've been using for all of my SSD tests, I created a 74.5GB RAID-0 array out of the two drives and quickly ran them through almost all of our benchmarks. At a total cost of $250, a pair of X25-Vs will set you back more than a single 80GB X25-M and you do give up TRIM, but is the performance worth it?

The Test

Sequential Read/Write Speed

Using the 6-22-2008 build of Iometer I ran a 3 minute long 2MB sequential test over the entire span of the drive. The results reported are in average MB/s over the entire test length:

This starts out very interesting. Each SATA port on our X58 board is bound by a 3Gbps transfer limit, but run two in parallel and you can go much higher. Our pair of X25-Vs are actually faster than Crucial's RealSSD C300 on a 6Gbps controller! That's absolutely nuts.

Sequential write speed also shows a near doubling of performance, unfortunately that only brings us up to ~84MB/s. It's not bad for most users but if you do a lot of heavy downloading or file copying, you'll still be behind an Indilinx, Crucial or SandForce drive.

Random Read/Write Speed

This test reads/writes 4KB in a completely random pattern over an 8GB space of the drive to simulate the sort of random access that you'd see on an OS drive (even this is more stressful than a normal desktop user would see). I perform three concurrent IOs and run the test for 3 minutes. The results reported are in average MB/s over the entire time.

I've had to run this test two different ways thanks to the way the newer controllers handle write alignment. Without a manually aligned partition, Windows XP executes writes on sector aligned boundaries while most modern OSes write with 4K alignment. Some controllers take this into account when mapping LBAs to page addresses, which generates additional overhead but makes for relatively similar performance regardless of OS/partition alignment. Other controllers skip the management overhead and just perform worse under Windows XP without partition alignment as file system writes are not automatically aligned with the SSD's internal pages.

First up is my traditional 4KB random write test, each write here is aligned to 512-byte sectors, similar to how Windows XP might write data to a drive:

In sector-aligned 4K random writes, nothing is faster than our X25-V RAID 0 array. We're talking faster than Intel's X25-E, faster than SandForce...you get the picture.

Our 4K aligned test, more indicative of random write performance under newer OSes puts a damper on the excitement:

At 71.6MB/s we're definitely faster than any other Intel drive here, as well as the 50GB SandForce offerings. But still no where near as fast as the C300 or OCZ Vertex LE.

Random read performance didn't improve all that much for some reason. We're bottlenecked somewhere else obviously.

Overall System Performance using PCMark Vantage

Next up is PCMark Vantage, another system-wide performance suite. For those of you who aren’t familiar with PCMark Vantage, it ends up being the most real-world-like hard drive test I can come up with. It runs things like application launches, file searches, web browsing, contacts searching, video playback, photo editing and other completely mundane but real-world tasks. I’ve described the benchmark in great detail before but if you’d like to read up on what it does in particular, take a look at Futuremark’s whitepaper on the benchmark; it’s not perfect, but it’s good enough to be a member of a comprehensive storage benchmark suite. Any performance impacts here would most likely be reflected in the real world.

Intel had been falling behind in the PCMark Vantage charts thanks to the SandForce and Crucial drives, but RAIDing these two X25-Vs makes up for a lot of lost time. Overall performance is basically on par with the entry level SandForce drives, but behind the C300 on a 6Gbps controller. The rest of the tests have the X25-V landing either in the middle or near the top of the charts, not bad for $250.

The memories suite includes a test involving importing pictures into Windows Photo Gallery and editing them, a fairly benign task that easily falls into the category of being very influenced by disk performance.

The TV and Movies tests focus on on video transcoding which is mostly CPU bound, but one of the tests involves Windows Media Center which tends to be disk bound.

The gaming tests are very well suited to SSDs since they spend a good portion of their time focusing on reading textures and loading level data. All of the SSDs dominate here, but as you'll see later on in my gaming tests the benefits of an SSD really vary depending on the game. Take these results as a best case scenario of what can happen, not the norm.

In the Music suite the main test is a multitasking scenario: the test simulates surfing the web in IE7, transcoding an audio file and adding music to Windows Media Player (the most disk intensive portion of the test).

The Communications suite is made up of two tests, both involving light multitasking. The first test simulates data encryption/decryption while running message rules in Windows Mail. The second test simulates web surfing (including opening/closing tabs) in IE7, data decryption and running Windows Defender.

I love PCMark's Productivity test; in this test there are four tasks going on at once, searching through Windows contacts, searching through Windows Mail, browsing multiple webpages in IE7 and loading applications. This is as real world of a scenario as you get and it happens to be representative of one of the most frustrating HDD usage models - trying to do multiple things at once. There's nothing more annoying than trying to launch a simple application while you're doing other things in the background and have the load take forever.

The final PCMark Vantage suite is HDD specific and this is where you'll see the biggest differences between the drives:

AnandTech Storage Bench

The first in our benchmark suite is a light usage case. The Windows 7 system is loaded with Firefox, Office 2007 and Adobe Reader among other applications. With Firefox we browse web pages like Facebook, AnandTech, Digg and other sites. Outlook is also running and we use it to check emails, create and send a message with a PDF attachment. Adobe Reader is used to view some PDFs. Excel 2007 is used to create a spreadsheet, graphs and save the document. The same goes for Word 2007. We open and step through a presentation in PowerPoint 2007 received as an email attachment before saving it to the desktop. Finally we watch a bit of a Firefly episode in Windows Media Player 11.

There’s some level of multitasking going on here but it’s not unreasonable by any means. Generally the application tasks proceed linearly, with the exception of things like web browsing which may happen in between one of the other tasks.

The recording is played back on all of our drives here today. Remember that we’re isolating disk performance, all we’re doing is playing back every single disk access that happened in that ~5 minute period of usage. The light workload is composed of 37,501 reads and 20,268 writes. Over 30% of the IOs are 4KB, 11% are 16KB, 22% are 32KB and approximately 13% are 64KB in size. Less than 30% of the operations are absolutely sequential in nature. Average queue depth is 6.09 IOs.

The performance results are reported in average I/O Operations per Second (IOPS):

That's right. A pair of X25-Vs in RAID-0 offers better performance in our light workload than Crucial's RealSSD C300, a $799 drive. The performance scaling is more than perfect, but that's a side effect of the increase in capacity. Remember that Intel's controller uses any available space on the SSD as spare area to keep write amplification at a minimum. Our storage bench is based on a ~34GB image, which doesn't leave much room for the 40GB X25-V to keep write amplification under control. With two our total capacity is 74.5GB, which is more than enough for this short workload. With the capacity cap removed, the X25-Vs can scale very well. Not nearly twice the performance of an X25-M G2, but much faster than a single drive from Intel.

If there’s a light usage case there’s bound to be a heavy one. In this test we have Microsoft Security Essentials running in the background with real time virus scanning enabled. We also perform a quick scan in the middle of the test. Firefox, Outlook, Excel, Word and Powerpoint are all used the same as they were in the light test. We add Photoshop CS4 to the mix, opening a bunch of 12MP images, editing them, then saving them as highly compressed JPGs for web publishing. Windows 7’s picture viewer is used to view a bunch of pictures on the hard drive. We use 7-zip to create and extract .7z archives. Downloading is also prominently featured in our heavy test; we download large files from the Internet during portions of the benchmark, as well as use uTorrent to grab a couple of torrents. Some of the applications in use are installed during the benchmark, Windows updates are also installed. Towards the end of the test we launch World of Warcraft, play for a few minutes, then delete the folder. This test also takes into account all of the disk accesses that happen while the OS is booting.

The benchmark is 22 minutes long and it consists of 128,895 read operations and 72,411 write operations. Roughly 44% of all IOs were sequential. Approximately 30% of all accesses were 4KB in size, 12% were 16KB in size, 14% were 32KB and 20% were 64KB. Average queue depth was 3.59.

We see the same super scaling here thanks to the increase in capacity offered by RAIDing two of these drives together. The overall performance is great. We're at around 91% better performance than a single X25-M G2.

The gaming workload is made up of 75,206 read operations and only 4,592 write operations. Only 20% of the accesses are 4KB in size, nearly 40% are 64KB and 20% are 32KB. A whopping 69% of the IOs are sequential, meaning this is predominantly a sequential read benchmark. The average queue depth is 7.76 IOs.

As we saw in our sequential read tests, the X25-Vs in RAID-0 can do very well in sequential read workloads. Our game loading test has the X25-V RAID array beating even Crucial's 6Gbps RealSSD C300.

Missing TRIM - Does it Matter?

Clearly the performance of two X25-Vs in RAID 0 is great, but you do lose TRIM - isn't that a dealbreaker? Honestly, it depends. For sequential accesses, TRIM isn't necessary on the Intel drives. The X25 controller does a good job of aggressively cleaning and recycling NAND blocks and you'll pretty consistently write at peak performance if your workload is almost all sequential.

The more random your access pattern is, the more you'll miss TRIM. Thankfully desktops don't spend too much of their time randomly writing data across the drive, but I'd say a good 30% of most desktop writes are random to an extent. Over time, these random writes will build up and bring down the overall performance of your RAID array until you either secure erase the drives or write sequentially to all available free space.

There is one other option for curbing the performance degradation before it happens. Remember the relationship between spare area and write amplification:

The more random your workload, the higher your write amplification (and thus the lower your performance, shorter your NAND lifespan). Increasing spare area can go a long way to reducing write amplification. While it can't eliminate it, it can definitely make a dent.

If you're looking to keep performance as high as possible with a pair of X25-Vs in RAID, you can always allocate more NAND as spare area. Secure erase each drive, create your RAID array, and then create your partition on the drive smaller than max capacity (try 10 - 20% smaller). The unpartitioned space should automatically be used by the controller as spare area. To test the effectiveness of this approach I took an X25-V, filled it with garbage data, and then wrote random data across the drive as fast as possible for 20 minutes. I then ran HD Tach to get a visualization of write latency (expressed by sudden drops in bandwidth) vs. LBA:

A standard 80GB X25-M wouldn't be this bad off, the X25-V gets extra penalized by having such a limited capacity to begin with. You can see that the drive is attempting to write at full speed but gets brought down to nearly 0MB/s as it has to constantly clean dirty blocks. Constant TRIMing would never let the drive get into this state. It's worth mentioning that a desktop usage pattern shouldn't get this happen either. Another set of sequential writes will clean up most of this though:

Intel's controller is very resillient. Even without TRIM, as long as your access pattern has some amount of a sequential component you'll be able to eventually recover performance.

Now look at what happens if we only use 60GB of the 74.5GB RAID 0 array upon creation and run the same test:

Performance isn't nearly as bad. That added spare area really comes in handy. Of course another pass corrects nearly everything:

If you don't need the added space, using a smaller partition is a great way to ensure high performance for as long as possible. The effectiveness of this approach is a difficult thing to benchmark given that it's only after months of normal use that you get enough random writes to the drive to be a problem. The good news is that even if you bombard the X25-Vs with random writes, the drives can quickly recover as soon as they're hit with some sequential data.

Final Words

While I can't say that I like the idea of giving up TRIM support, the performance you get out of a pair of X25-Vs in RAID 0 is impressive. You effectively get next-generation controller performance out of a tweaked version of a 2 year old SSD. The lack of TRIM does bother me, but I personally use an X25-M G2 under OS X without TRIM and the drive is resilient enough (most of the time) to not make me feel any performance degradation.

Given the price point and the well behaved nature of these drives, I'd say it's definitely worth your consideration. If you like the simplicity of a single drive setup or want to hang on to TRIM support (perhaps if you do know your workload is more random than normal), by all means go for a single G2 or one of the SandForce offerings. However, if you're fine dealing with a potentially more complex setup (if one of your X25-Vs dies, you lose all your data) and don't mind giving up TRIM, this is a great option. The X25-V RAID 0 route gives you all of the Intel SSD safety net while posting some very competitive numbers. At $250 it may be the best overall performance you get out of an SSD at this price point until Intel's 3rd generation drives ship in Q4.

It's high performance on a budget, not without its tradeoffs, but in this case they may be livable.