|SandForce SF1200 RAID-0 SSD Performance|
|Reviews - Featured Reviews: Storage|
|Written by Olin Coles|
|Tuesday, 04 May 2010|
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SSD Testing Methodology
Solid State Drives have traveled a long winding course to finally get where they are today. Up to this point in technology, there have been several key differences separating Solid State Drives from magnetic rotational Hard Disk Drives. While the DRAM-based buffer size on desktop HDDs has recently reached 32 MB and is ever-increasing, there is still a hefty delay in the initial response time. This is one key area in which flash-based Solid State Drives continually dominates because they lack moving parts to "get up to speed".
However the benefits inherent to SSDs have traditionally fallen off once the throughput begins, even though data reads or writes are executed at a high constant rate whereas the HDD tapers off in performance. This makes the average transaction speed of a SSD comparable to the data burst rate mentioned in HDD tests, albeit usually lower than the HDD's speed.
Comparing a Solid State Disk to a standard Hard Disk Drives is always relative; even if you're comparing the fastest rotational spindle speeds. One is going to be many times faster in response (SSDs), while the other is usually going to have higher throughput bandwidth (HDDs). Additionally, there are certain factors which can affect the results of a test which we do our best to avoid.
RAID-0 Stripe Mode
This article presents two opposing views: one set of results using RAID-0 configured with 4KB stripe sizes, and the other using Intel's ICH10 maximum of 128KB stripes. Many PC hardware enthusiasts ask which RAID-0 stripe size is better, without understanding the implications involved with the answer. There are countless variables that could make one size perform better than another and a magnetic hard drive, but for solid state storage products the response time is up to 450x faster and therefore has less impact on performance. More often than not, the size of files stored on the drive are the key indicator behind the appropriate RAID-0 stripe size.
Each stripe of data is a specific size. If a stripe size is set to 4KB, then a 4KB file would be written by only one drive using a single stripe. However, if that file is 8KB, then it would be split in half and written to both drives. Not many files are as small as 4KB anymore, which creates a storage processing penalty when larger files are written. For example, if a 4KB stripe is assigned and a 4MB file is written, then 500 date stripes are written to each drive. When these same drives are assigned a 128KB stripe size, each drive is written to only 31 times. This may create the illusion that larger stripe file sizes are better, but SSDs could possibly change this dynamic.
SSD Testing Disclaimer
Early on in our SSD coverage, Benchmark Reviews published an article which detailed Solid State Drive Benchmark Performance Testing. The research and discussion that went into producing that article changed the way we now test SSD products. Our previous perceptions of this technology were lost on one particular difference: the wear leveling algorithm that makes data a moving target. Without conclusive linear bandwidth testing or some other method of total-capacity testing, our previous performance results were rough estimates at best.
Our test results were obtained after each SSD had been prepared using DISKPART or Sanitary Erase tools. As a word of caution, applications such as these offer immediate but temporary restoration of original 'pristine' performance levels. In our tests, we discovered that the maximum performance results (charted) would decay as subsequent tests were performed. SSDs attached to TRIM enabled Operating Systems will benefit from continuously refreshed performance, whereas older O/S's will require a garbage collection (GC) tool to avoid 'dirty NAND' performance degradation.
It's critically important to understand that no software for the Microsoft Windows platform can accurately measure SSD performance in a comparable fashion. Synthetic benchmark tools such as HD Tach and PCMark are helpful indicators, but should not be considered the ultimate determining factor. That factor should be measured in actual user experience of real-world applications. Benchmark Reviews includes both bandwidth benchmarks and application speed tests to present a conclusive measurement of product performance.
Drive Hardware Tested
The following storage hardware has been used in our benchmark performance testing, and may be included in portions of this article:
Test Results Disclaimer
This article utilizes benchmark software tools to produce operational IOPS performance and bandwidth speed results. Each test was conducted in a specific fashion, and repeated for all products. These test results are not comparable to any other benchmark application, neither on this website or another, regardless of similar IOPS or MB/s terminology in the scores. The test results in this project are only intended to be compared to the other test results conducted in identical fashion for this article.