by Robert Tanner on August 23, 2010 in Solid-State Drives
Looking to upgrade your PC with a fast SSD? How fast do you want it? If you answered “ultra fast”, then OCZ’s RevoDrive is worth a look. With read speeds of 500MB/s and beyond, a PCI Express interface, and a modest price premium, this SSD is hard to ignore. We’re on the bleeding-edge here, though, so this drive isn’t without a few caveats.
Originally developed by Intel, and since given to the open-source community, Iometer (pronounced “eyeawmeter”, like thermometer) is one of the best storage-testing applications available, for a couple of reasons. The first, and primary, is that it’s completely customizable, and if you have a specific workload you need to hit a drive with, you can easily accomplish it here. Also, the program delivers results in IOPS (input/output operations per second), a common metric used in enterprise and server environments.
The level of customization cannot be understated. Aside from choosing the obvious figures, like chunk sizes, you can choose the percentage of the time that each respective chunk size will be used in a given test. You can also alter the percentages for read and write, and also how often either the reads or writes will be random (as opposed to sequential). I’m just touching the surface here, but what’s most important is that we’re able to deliver a consistent test on all of our drives, which increases the accuracy in our results.
Because of the level of control Iometer offers, we’ve created profiles for three of the most popular workloads out there: Database, File Server and Workstation. Database uses chunk sizes of 8KB, with 67% read, along with 100% random coverage. File Server is the more robust of the group, as it features chunk sizes ranging from 512B to 64KB, in varying levels of access, but again with 100% random coverage. Lastly, Workstation focuses on 8KB chunks with 80% read and 80% random coverage.
Because these profiles aren’t easily found on the Web, with the same being said about the exact structure of each, we’re hosting the software here for those who want to benchmark their own drives with the exact same profiles we use. That ZIP archive (~3.5MB) includes the application and the three profiles in an .icf file.
Scenarios such as these are pretty much the bane of hard drives and illustrate why 15,000RPM SCSI drives exist. Ironically, despite Iometer and these tests being created well before SSDs began entering the desktop market, the nature of the tests are going to inherently favor them due to their rapid, near-instantaneous random access times. While we do not have a 15,000RPM or VelociRaptor drive to use for reference, the numbers generated by them would only be little better than the desktop drive results.
If looking for a perfect test to illustrate the potential strengths of random access, this would be it. That said, the large number of 512B to 4KB mixed reads and writes in the File Server scenario will also be the anathema of any SSD controller that was designed primarily for large sequential read & write performance. We can gauge which candidates have the highest potential to suffer from performance stuttering with these tests. Very small, random file operations are the worst offenders as they stress the controller the most.
If the SSD controller becomes backlogged, it will exacerbate the stuttering, causing file operations that should take milliseconds to instead take up to a full second or more to complete, thereby only compounding the problem. Of course when there are not one but two SF-1200 SandForce controllers that can evenly divide the workload, it becomes much harder to saturate the drive. The sheer power of the SF-1200 controller combined with two of them to split the workload means even these daunting workloads are easily taken in stride.
As the name might hint, AS SSD is a nifty little program written exclusively for SSDs. It can be run on mechanical hard drives, but be warned that what should take minutes will take over an hour to benchmark! This handy little tool provides several read/write tests at important file sizes, but also includes a benchmark to simulate the transfer of three types of large files.
We selected this program for its precision, ability to generate large file sizes on the fly, and that it is written to bypass Windows 7’s automatic caching system. The tool does not bypass any onboard cache.
Although several of the results are close, the RevoDrive again walks away with the final score results. Here’s a good point to mention that access times like these are the reason why a mechanical disk RAID array can never be the equal of any good quality SSD. Adding mechanical drives together in RAID does not decrease the initial access latency involved. Concurrent file accesses in RAID can better hide the latency penalty, but it doesn’t actually remove it. In the same way the same is true of the Revo, although two SF-1200 controllers are present in RAID 0, the access times are identical to that of the single SF-1200 controller found in the Vertex 2 SSD.