4K Random Read/Write
We precondition the SSDs for 18,000 seconds, or five hours, receiving reports on several parameters of workload performance every second. We then plot this data to illustrate the drives' descent into steady state. This chart consists of 36,000 data points. The dots are IOPS measurements during the preconditioning period. The lines through the data scatter are the average during the test. This type of testing presents standard deviation and maximum/minimum I/O in a visual manner.
We provide histograms for further latency granularity below. This downward slope of performance happens very few times in the lifetime of the device, during the first few hours of use, and we typically only present the precondition results to confirm steady state convergence. In this article, we are combining the preconditioning runs to highlight the performance of consumer products.
The OCZ Vector and the Samsung 840 Pro suffer from significant performance variability. The wide swath of results points to varying performance during the preconditioning period. The SMART Optimus holds steady with very little variability.
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 4K random read performance of the OCZ Vector rises above the Optimus, while the 840 Pro resides at a lower value of 70,000 IOPS. The Vector performs admirably in the pure random read environment. However, during actual deployment into an enterprise environment, a pure read workload is rare.
Garbage collection routines are more pronounced in heavy write workloads. This leads to more variability in performance, and the difference between the Optimus and the consumer SSDs is very clear with this test. The client SSDs suffer from tremendous variability, and average well below a third of the performance of the Optimus. Much like pure read environments, a pure write workload is equally rare.
Our write percentage testing illustrates the varying performance of each solution with mixed workloads. The 100% column to the right is a pure write workload of the 4K file size, and 0% represents a pure 4K read workload.
The massive read performance of the Vector is brought down to earth in this testing, illustrating one of the key differences between client and enterprise SSDs. Enterprise hardware is designed to handle heavy write workloads with ease, and here we can see that the client SSDs suffer a drastic reduction in performance with even the slightest of write workloads.
The Vector averages 97,000 IOPS with a pure read workload, but this drops dramatically to 27,000 IOPS with the introduction of only 10% writes into the workload. The 840 Pro suffers a comparable loss, from 70,000 IOPS to 22,000. The Optimus also loses speed as we mix in more writes into the workload, but we can see that the reduction in performance is not near the scale suffered by the client SSDs.
Observing the distribution of latency during the test period also brings into focus one of the overlooked aspects of performance. The latency of the requests is extremely important, and one of the key advantages of using an SSD over an HDD.
The massive distribution of latency from the client SSDs is a tangible problem that will have a direct impact upon application performance. Both the Vector and the 840 Pro suffer a significant number of outlying I/O's that take longer than 200-400ms to complete. Our charts only go to 200-400ms, but the Vector had several I/O's land as high as 600-800ms, and the 840 Pro has operations in the 800-1000ms range.
We record the power consumption measurements during our precondition run. We calculate the stated average results during the last five minutes of the test, after the device has settled into steady state.
To the untrained eye, the power requirement of the Optimus is drastically higher than that of the client SSDs. While the Optimus does require more power for operation, it accomplishes much more work with the same amount of voltage, as covered in the graph below.
IOPS to Watts measurements are generated from data recorded during our precondition run, and the stated average is from the last five minutes of the test.
The IOPS to Watts measurements gauge the efficiency of the SSD during the workload, and calculates the amount of work accomplished per Watt. As noted above, the Optimus does require significantly more power to operate, but the amount of IOPS provided per Watt reveals that the Optimus is actually more efficient than the Vector and the 840 Pro.