Results: Tom's Hardware Storage Bench v1.0, Continued
Service Times
Beyond the average data rate reported on the previous page, there's even more information we can collect from Tom's Hardware's Storage Bench. For instance, mean (average) service times show what responsiveness is like on an average I/O during the trace.
It would be difficult to graph the 10+ million I/Os that make up our test, so looking at the average time to service an I/O makes more sense. For a more nuanced idea of what's transpiring during the trace, we plot mean service times for reads against writes. That way, drives with better latency show up closer to the origin; lower numbers are better.
Write latency is simply the total time it takes an input or output operation to be issued by the host operating system, travel to the storage subsystem, commit to the storage device, and have the drive acknowledge the operation. Read latency is similar. The operating system asks the storage device for data stored in a certain location, the SSD reads that information, and then it's sent to the host. Modern computers are fast and SSDs are zippy, but there's still a significant amount of latency involved in a storage transaction.
When we get four models from the same product family split between a range of capacities, it's not uncommon for there to be a big delta between the smallest and largest drives.
For the most part, our tests show that read performance is similar on each drive, even though the 128 GB SP920 is just one-eighth the size of the 1024 GB model. Writes take a massive hit, though, since the smaller SSDs employ fewer dies to spread workloads across.
Mean Read Service Time
Adata's SP920s demonstrate similar read performance as the other SSDs equipped with IMFT's flash.
Finally, Adata's SP920s are vindicated. The 1024 GB model beats out the largest M550 for first place. No desktop-oriented SSD we've tested boasts such an excellent result. Yes, the margin of victory is tiny, but you can see just how compelling the competition is, as well.
And we're again presented by a mystery in the 512 GB SP920. It isn't at the top of the chart alongside Crucial's M550, which is itself identical to the 1024 GB model. The difference is notable enough for us to think twice about some of the assumptions we've made about the data generated thus far. We're not talking about a crazy deficit or anything, but the drive is marginally slower in our trace-based testing. Just bear in mind that you'd have a hard time telling a difference in a real-world workload.
The 128 GB SP920 beats Samsung's 120 GB 840 EVO and Crucial's M500 at the same capacity point, which is a testament to Marvell's updated controller. Both competing SSDs use 128 Gb die as well.
