RAID 0 4K Random Read/Write
We precondition both 64K stripe RAID 0 arrays, with 8 and 4 x 200GB Intel DC S3700 SSDs, for 18,000 seconds, or five hours, receiving reports on several parameters of workload performance every second. We plot this data to illustrate the drives' descent into steady state.
This chart consists of 16,000 data points. The dots signify IOPS performance every second during the test. The lines through the data scatter represent the average performance during the test. This type of testing presents standard deviation and maximum/minimum I/O in a visual manner.
High-granularity testing can give our readers a good feel for the latency distribution by viewing IOPS at one-second intervals. This should be in mind when viewing our test results below. We provide latency charts for further granularity below.
This downward slope of performance happens very few times in the lifetime of the device, typically during the first few hours of use, and we present the precondition results only to confirm steady state convergence.
Each QD for every parameter tested includes 300 data points (five minutes of one second reports) to illustrate the degree of performance variability. The line for each QD represents the average speed reported during the five-minute interval.
4K random speed measurements are an important metric when comparing drive performance, as the hardest type of file access for any storage solution to master is small-file random. One of the most sought-after performance specifications, 4K random performance is a heavily marketed figure.
The 8-drive array peaks at an average of 480,269 IOPS at QD256, while the 4-drive array reaches 248,753 IOPS. The 8-drive array falls shy of linear scaling, but averages an output of 60,000 IOPS per SSD.
Our read latency chart reveals that the four drive array latency nearly doubles in the jump from QD128 (2.06ms) to QD256 (4.05ms). This doubling of latency reaps only a minor performance gain in IOPS, as shown in the chart above the latency chart. This indicates that limiting the array to QD128 would provide optimum performance in both IOPS and latency for a read-centric 4K workload in some latency-sensitive environments.
Garbage collection routines are more pronounced in heavy write workloads. This leads to more variability in performance.
The Intel DC S3700 8-drive array produces an average of 252,177 IOPS at QD256, or roughly 31,522 per SSD. This is near-perfect write scaling, with the specifications for the 200GB SSDs at 32,000 IOPS each. The 4-drive array averages 130,703 IOPS at QD256, or 32,675 IOIPS per SSD, slightly above the rated specifications.
The write latency charts illustrated the scaling for the 8-drive array is optimum for IOPS/latency at QD128, and QD64 for the 4-drive array.