Samsung SSD 850 EVO (120GB, 250GB, 500GB & 1TB) Reviewby Kristian Vättö on December 8, 2014 10:00 AM EST
Endurance: Close to Planar MLC NAND
The big question with every new NAND generation is the endurance. We already saw 6,000 P/E cycles in the SSD 850 Pro and an amazing 40,000 P/E cycles in the SSD 845DC Pro, which proved that V-NAND provides substantially better endurance over today's planar NAND nodes. However, endurance was never really an issue with planar MLC NAND except in the enterprise space, so the 850 EVO with its TLC V-NAND offers a much more interesting insight to the capability of 3D NAND technology.
To test endurance, I put the 120GB 850 EVO through our usual endurance test suite. Basically I just used Iometer to write 128KB sequential data at queue depth of 1 to the drive while monitoring the Wear Leveling Count (WLC) and Total LBAs Written SMART values. The 'Current Value' of the WLC SMART value gives the remaining endurance as a percentage (starts from 99), whereas the 'Raw Data' value indicates the number of consumed P/E cycles. In order to estimate the endurance, I had to find the spot where the increase in 'Raw Data' value decreases the 'Current Value' by one.
|Samsung SSD 850 EVO Endurance|
|Change in Current Wear Leveling Count Value||6|
|Change in Raw Wear Leveling Count Value||128|
|Total Data Written||15,260GiB|
|Estimated Total Write Endurance||254,325GiB|
|Observed Number of P/E Cycles||1,987|
It appears that TLC flavor of V-NAND is rated at about 2,000 P/E cycles. The raw WLC value seems to be based on the user capacity (i.e. 120GB = 1 P/E cycle) because just going by it puts the endurance at ~2,133 P/E cycles (128/0.06), but that doesn't add up with the raw NAND capacity and total data written. However, the estimated total write endurance (which is just 15,260/0.06) suggests that the NAND itself is rated at 2,000 P/E cycles, which would make sense as the number of P/E cycles is usually an even thousand and it's also inline with the increase that the 850 Pro saw (from 3,000 cycles in the 840 Pro to 6,000 cycles).
|Samsung SSD 850 EVO Lifetime Estimation|
|Raw NAND Capacity||128GiB||256GiB||512GiB||1024GiB|
|NAND P/E Cycles||2,000|
|Raw NAND Endurance||250TiB||500TiB||1000TiB||2000TiB|
|Lifespan with 20GiB of Host Writes per Day with 1.5x Write Amplification||23.4 years||46.8 years||93.5 years||187.0 years|
|Lifespan with 100GiB of Host Writes per Day with 3x Write Amplification||2.3 years||4.7 years||9.4 years||18.7 years|
While write endurance in client workloads was never truly an issue even with planar TLC NAND, the doubled endurance in TLC V-NAND makes it practically impossible to wear out the drive before it has become totally obsolete. Only some very extreme workloads could wear out the smaller capacities before the warranty runs out, but the 850 EVO is a wrong drive for such workloads in the first place. All in all, there should be absolutely no reason to worry about the endurance of the 850 EVO, especially given the endurance ratings Samsung is giving to the 850 EVO (75TB for 120/250GB and 150TB for 500GB/1TB).