Test System and Methodology
We utilize a new approach to RAID storage testing with our Enterprise Test Bench, designed specifically to target long-term performance with a high level of granularity.
Many testing methods record peak and average measurements during the test period. 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 the 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.
While executing a workload, all storage solutions deliver variable levels of performance. While this fluctuation is normal, the degree of variability is what separates enterprise storage solutions from typical client-side hardware. Providing ongoing 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 directly 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 in this evaluation. This evaluation consists of tests with default settings conducted on a LSI 9271-8i with a direct connection. We conduct our tests over the full LBA range to allow each HDD to highlight its average performance. Short stroking can increase performance at the loss of capacity.
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