Test System and Methodology
We designed our approach to storage testing 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 Quality of Service (QoS).
'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.
While under load, 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 utilize high-granularity I/O latency charts to illuminate performance during our test runs.
Our testing regimen follows key SNIA principles to ensure consistent, repeatable testing. 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 test RAID 0 and RAID 5 for this evaluation. During testing, we noted periodic performance irregularities that occurred with both controllers at similar intervals. Due to the similar timing of performance errata with both controllers, we concluded these are GC or other internal functions of the HGST SSD test array.
We have found Serialcables.com to be a reliable source of high quality cables and accessories. We have a number of external SAS cables on hand for testing, but none that would fit the internal connectors on the RAID controller. The Dual HD MiniSAS Receptacle (SFF-8644) to Dual Int MD MiniSAS Plug (SFF-8643) allows conversion of internal to external ports. 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 has served us well.
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