Four-Corner Performance Testing
The 4TB 850 Evo doubles the capacity of the largest consumer SSDs currently shipping. There are only a few SSDs available with 2TB of storage, and two of the four are from Samsung (850 EVO and 850 Pro). Avant Technology manufactures a 2TB consumer drive that marries two 1TB consumer SSDs with a low-cost RAID controller, which then sell under the Mushkin and OWC brands. We included three of the four shipping 2TB SSDs in this review. We never received the Mushkin Reactor 2TB for review, but managed to secure an OWC Mercury Electra 2TB that should provide the same performance.
Sequential Read Performance
You will not see a lot of variance in performance between the three Samsung products until later in this review. For the most part, the new 850 EVO delivers the same performance that we measure in the 2TB 850 Pro and EVO review. The OWC Mercury Electra 2TB falls well short of hitting the high bar set by the three Samsung 850 products.
Sequential Write Performance
Products armed with three-bit per cell NAND flash usually have trouble with large sequential write tests. We often see large swings in performance that appear on the charts as waves, which is due to the data passing between the SLC and TLC areas. The Samsung 850 EVO 4TB is so large that you will write all data to the SLC area unless you run the drive nearly full. It would be very difficult to force a steady state condition under normal use with a large 96GB SLC spare area.
Random Read Performance
The Samsung 850 EVO 4TB sets the bar very high for random read performance at low queue depths. Samsung lists a very generic 10,000 IOPS rating for the latest EVO SSD, but there is more to the story. The 850 Evo delivers the highest queue depth 1 random performance of any SATA SSD we've ever tested; the SSD nearly surpassed 12,000 IOPS. To put this into perspective, the new Samsung SM961 NVMe PCIe SSD only reaches 15,000 IOPS. With this much random read performance, the new 850 EVO 4TB may overtake the SanDisk Extreme Pro as the fastest SATA SSD ever made.
Random Write Performance
The three Samsung 850 products deliver nearly identical random write performance results, too. At this point, you may wonder what is so "Pro" about the 850 Pro. It appears that Samsung asked the same question and decided to either wait or cancel the update for the 850 Pro series at this time.
What we see is the SLC mode buffer absorbing all of the random writes and then rolling the data to the TLC area. We've talked about this in the past but should mention it again. Samsung's 3D TLC flash is much faster than 2D MLC from SK Hynix, Toshiba, SanDisk, Intel and Micron, so it is better to compare Samsung's TLC to MLC NAND from every other company. Even Micron's new 3D TLC with 384bit die is slower than Samsung's 3D TLC flash.