Samsung 860 Evo & 860 Pro SSD review: the counterattack!

Samsung also refreshes complete SATA lineup of SSDs

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Continuous activity tests - Steady State Performance

The steady state performance of an SSD, or the performance level at which an SSD stabilizes after a long period of intensive use, is especially important to individuals who are going to use an SSD for professional applications, such as workstation or server applications.

Let's start off with some background information. We have mentioned numerous times that data on SSDs can be written and read per so-called page, which are usually quantities of 4, 8, or 16 kB. However, in order to write data, data cells have to be erased first, and that can only be done per block. Each block consists of 128, 256, or 512 pages. As a result, SSDs have to resort to clever tricks. When a number of pages worth of data has to be erased, the SSD first has to copy the rest of the data in the block to another block, after which the entire block can be erased. In practice, this means that SSD controllers collect as many write actions as possible, and then simultaneously perform them on new, freshly emptied blocks. At the same time, delete actions are only performed at specific moments. At these moments, when the SSD is idle, the controller enables the built-in garbage collector, which actually performs the delete actions on a chip level and whenever possible combines the leftover data in full blocks, in order to maximize the amount of blocks that can be fully emptied.

However, when the SSD is being used continuously for a long period of time, that is to say, without even a second of idle time, the garbage collector is simply unable to do its thing. As a result, the SSD will run out of empty blocks at a certain point in time, which means that it has to resort to performing garbage collection in between commands. Naturally, this results in lower performance. The performance level at which an SSD stabilizes in such a scenario is referred to as its steady state performance.

We run two different continuous activity tests to determine this steady state performance. Both tests are run using Iometer, where we continuously run each workload for a period of 30 minutes and report the average performance over each minute. The first continuous activity test is the 4k random write QD32 benchmark. The second continuous activity test is the Iometer database workload simulation, also ran using a queue depth of 32. Both tests are run on a test file that takes up 75% of the drive's capacity (LBA).

4kB random write QD32

In our continuous testing, the Samsung 860 Pros score worse than the older 850 Pros, which were undisputedly the leaders of this chart. The scores of about 130 MB/s are still nothing that Samsung should be ashamed of, but less special than those of their predecessors. Meanwhile, the 860 Evo's are performing as well as the 850 Evo's. It is worth noting, however, that the 1TB variants of both SSDs continue to perform at their maximum for longer than the 500GB editions.

Database simulation QD32

In the long-term database simulation, the 860 Pros do show what they're capable of. In the first 30 minutes of this ten-hour test, shown in the line chart below, the 860 Pro 1TB does not even collapse to its steady-state level. If we look at the last 20 minutes, however, it comes out at 208 MB/s, with which he still proudly sits on top of the graph. It should be noted, however, that the Crucial MX500's are awfully close to it - the 1TB version of that series ends at 196 MB/s.

When we tested the 850 Evo's, we did not carry out the ten-hour version of this test on SSDs yet. When we look at the first 30 minutes, however, they seem to be almost identical to the new 860 Evos.


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