Test System and Methodology
We utilize a new approach to RAID storage testing designed specifically to target performance with a high level of granularity. Many testing methods record peak and average measurements. These average values give a basic understanding of performance, but fall short in providing the clearest view possible of I/O QoS (Quality of Service).
'Average' results do little to indicate performance variability experienced during actual deployment. The degree of variability is especially pertinent, as many applications can hang or lag as they wait for I/O requests to complete. This testing methodology illustrates performance variability, and includes average measurements, during the measurement window. Providing measurements from our workloads with one-second reporting intervals illustrates product differentiation in relation to I/O QoS. Scatter charts give readers a basic understanding of I/O latency distribution without observing numerous graphs.
Consistent latency is the goal of every storage solution, 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 consider latency distribution, but do not always effectively illustrate I/O distribution with enough granularity to provide a clear picture of system performance. We also use latency plots to illustrate latency scaling under various workloads.
The first page of results will provide the 'key' to understanding and interpreting our new test methodology. In replicated environments, RAID 0 can be a compelling choice for bleeding edge performance. RAID 5 provides a layer of data security that protects from the loss of a drive. We are testing both RAID 0 and RAID 5 for this evaluation. Bear in mind that the test results of the prototype may not reach the maximum capabilities of the production-run ASR-8885.
To test performance with 12Gb/s SSDs we selected the fastest SSD available on the market, the HGST SSD800MH SSD's. Eight of these SSDs are powerful enough to saturate even the fastest of controllers. We have written a product evaluation of the slightly slower version of this SSD, the HGST SSD800MM SSD's. Look to these pages soon for an evaluation of the SSD800MH, which features sequential read/write speeds of 1200/750 MB/s and read/write IOPS of 145,000/100,000 IOPS.
Our array of 26 of the 6Gb/s 400GB Micron P400m's will be a staple in all RAID product evaluations moving forward. The demanding nature of our enterprise test lab requires resilient solid state storage for testing, and we selected the P400m specifically due to its consistent performance and heavy endurance capabilities. Top speeds of 60,000/26,000 read/write IOPS and up to 380/310 MB/s of sequential throughput allow the P400m's to push 6Gb/s devices to the limit. We have already published the Micron P400m 200GB Enterprise SSD Evaluation, and look to these pages soon for a product evaluation with 24 of these SSD's in various RAID configurations.
Adaptec by PMC manufacturers HD MiniSAS cables, on the left of the picture, which are available through their resellers. The Adaptec cables are high quality, but only available in mainstream configurations.
For other cabling needs, such as the external to SAS breakouts in the middle and the dual-port SAS cables to the right, we have found Serialcables.com to be a reliable source of high quality cables and accessories. Serial Cables has mainstream, specialty, and limited availability items in stock. When working under deadlines, and tight schedules, the fast service and knowledgeable staff at Serial Cables have served us well.