Nearly all of the drives in our comparison charts utilize TLC NAND with write enhancement mechanisms to deliver high burst speeds that are not sustainable for more than a few seconds.
Samsung's SSD 850 EVO is the current mid-range performance leader. Its quad-plane TLC flash breaks the mold and delivers longer sustained write speeds than other TLC-based drives with flash from Toshiba and Micron. The Plextor M6V is a newer model that uses the same approach as the Reactor. It comes equipped with the same SMI SM2246EN controller, but pairs it with Toshiba's 15nm MLC NAND.
Sequential Read Performance
Even with eight levels of charge to sort through, nearly every drive hits the SATA interface's maximum performance level. As always, queue depth is important to consider, and we see more performance variation at the low queue depths encountered on a daily basis.
Samsung's 750 EVO 250GB outperforms the 850 EVO, though the results indicate only a slight difference between both products. The 120GB 750 EVO does give up some sequential read speed at low queue depths compared to the other Samsung drives, but that's to be expected since it's working with half as many flash dies.
Sequential Write Performance
Samsung's TurboWrite algorithm performs well in our tests, even though we don't leave a lot of time for the buffer to flush between runs. Many competing products show up as waves, since they struggle to flush the emulated SLC buffer data to much slower TLC.
The third image illustrates the large block size sequential roll-off and sustained sequential write performance. Samsung's 750 EVO maintains writes in excess of 200 MB/s. Until recently, Samsung was the only vendor to hit that level using TLC NAND. Phison has caught up, though, with its direct-to-die write algorithm. We simply don't have a low-capacity Phison S10-based drive to add to our charts.
The 120GB SSD 750 EVO reaches the same performance in the buffer stage, but writes quickly drop to 140 MB/s after an extended load. TLC's native write speed won't become an issue until you need to send a lot of data to the drive at one time. Installing software and transferring large photo albums are two common examples of when you'd do that.
The emulated SLC buffer works to keep random performance high. Even though the SSD 750 EVO should be a very low-cost drive, it still delivers admirable random read results, which is important because most of your data transactions take the form of small-block reads and writes. The trade-off is a hit to endurance, which becomes an issue later in the product's life.
The 750 EVO and 850 EVO are separated by write performance. When we test with small blocks of data written randomly, the gap between them grows more than we saw in our sequential tests. Even at low queue depths, the two drives seem pretty similar to each other at any given capacity point. But as the queue depth increases, so does the 850 EVO's edge. Then again, the 250GB 750 EVO responds to our random write workload more favorably than the non-Samsung SSDs we benchmarked.