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Results: Tom's Hardware Storage Bench v1.0, Continued

SanDisk A110 PCIe SSD: Armed With The New M.2 Edge Connector
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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.

The A110 achieves phenomenally low write service times in this chaotic plot. Naturally, the explanation is fairly simple. Most of the read service time accumulated during the trace is a mix of random and sequential transfers, both small and large. Write requests predominantly include 4 KB random accesses and large-block size sequentials. Given a substantial advantage in sequential writes, the A110 services requests fast enough to put some distance between itself and the other 256 GB-class SATA SSDs.

It'd be wrong to characterize read service times as mostly the same for the drives we tested, but it's not fair to call them radically different, either. With that in mind, the A110 bests SanDisk's own Extreme II, though it doesn't quite land in the upper echelon.

Then again, with write performance like this, who cares? Write service times are far more varied anyway, demonstrating a range between a little more than 400 and more than 2500 microseconds. 

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