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Samsung 840 EVO SSD: Tested At 120, 250, 500, And 1000 GB

Results: Tom's Hardware Storage Bench, Continued

Service Times and Standard Deviation

Beyond the average data rate reported on the previous page, there's even more information we can collect from Tom'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. We can plot mean service times for reads against writes. That way, drives with better latency show up closer to the origin; lower numbers are better.

You really want to see your SSD serving up I/Os like a ninja tossing throwing stars (not altogether a bad analogy for I/O latency). He might be able to wing a number of them each second, but they all take time to reach their destination. If the host asks for a piece of data, how long does it take for the storage subsystem to respond with the right information? Splitting up read and write service times helps us understand each drive's strengths and weaknesses.

The 120 GB Samsung 840 EVO plots so far off the scale for writes that it's outside of our visible range.

All of the drives we're testing today demonstrate great mean read service times. Given their triple-level cell NAND, however, we have to give credit to Samsung's 840 EVOs for keeping up with the MLC-based competition.

The 840 Pro finishes just ahead of OCZ's Vector, and the 1 TB 840 EVO is just one microsecond behind. The 250 and 500 GB models fall in right after that, mixed in with the smaller 840 Pro, Intel's SSD 335, and the Vertex 450. Samsung's 120 GB 840 EVO is further back, though still in front of the 256 GB m4 and Neutron GTX.

This trace has over twice as many read IOs as writes. But writes account for more throughput. And even thought the three-bit-per-cell flash should be slower, Toggle-mode NAND and a faster controller could be keeping the 840 EVO competitive.

The 120 GB 840 EVO stands out for its high latency. On average, Samsung's entry-level model took 2.14 ms to sevice a request, which is three times longer than the first-place Vector.

In fact, two Indilinx-powered drives from OCZ take first and second place, while SanDisk's Extreme II snatches the bronze. The largest 840 EVOs land right in the middle, which isn't bad given Samsung's architecture and the write-heavy nature of our trace. Although the 840 EVOs don't lead the field, if nothing else, we're pleased to see triple-level cell NAND keeping up with the MLC competition.