The fun of testing HBA and RAID controllers is that we can use the fastest SSDs at our disposal in Fresh Out of Box (F.O.B.) conditions. One of the more tedious aspects of standard enterprise testing is the long drawn out conditioning runs to push the SSDs into steady state. This can take up to 12 hours for some SSDs, and consists of a lot of waiting on our part.
With HBA and RAID controller testing, we secure erase the SSDs repetitively to keep them at the absolute top speed. The ability to switch to the HBA mode with the ASR-72405 was a tremendous time saver when secure erasing the SSDs. There is obvious value to this functionality in mass deployments.
For throughput testing we turned to our trusty Crucial RealSSD C400s. Physically identical to the consumer M4, this 8 x 256GB array of SSDs has served us well in our testing by offering solid and consistent performance. We also had to bring in an additional 8 x 256GB M4's to help shoulder the load. Providing read speeds of 500 MB/s and 260 MB/s write speeds each, we can saturate the read bandwidth of the ASR-72405.
The second prong of our attack consists of the SanDisk ESS Lightning LS 300S EFDs (Enterprise Flash Devices). The LS 300S are 300GB SLC enterprise class SSDs that come in both a 3.5" and 2.5" form factor. These drives are made for taking a beating, and are warrantied for five years of unlimited writing with no throttling. They are simply solid as a rock, offering consistent performance regardless of the workload.
Rated at a blistering 160,000 IOPS per device, they are definitely the heavyweights of enterprise flash storage, even though we are using the 3Gb/s versions. There aren't many devices that can lay claim to this type of performance in steady state conditions.
Many forms of testing involve utilizing peak and average measurements over a given time period. While these average values can give a basic understanding of the performance of the storage solution, they fall short in providing the clearest view possible of the QOS (Quality of Service) of the I/O. The degree of variability is especially pertinent, as many applications can hang or lag as they wait for one I/O to complete.
Our testing illustrates the performance variability expected in these types of scenarios, including the average measurements, during the measurement window. By providing ongoing measurements from our workloads with one-second reporting intervals, we can illustrate the difference between different products in relation to the purity of the QOS.
Consistent latency is the goal of every storage device, and measurements such as Maximum Latency only illuminate the single longest I/O received during testing. This can be misleading, as a single 'outlying I/O' can skew the view of an otherwise superb solution. Standard Deviation measurements take the average distribution of the I/O into consideration, but do not always effectively illustrate the entire I/O distribution with enough granularity to provide a clear picture of system performance.
By utilizing scatter charts readers can gain a basic understanding of the latency distribution of the I/O stream without directly observing numerous graphs. We also present histograms to illuminate the latency of every single I/O during the measurement window.