Samsung SSD 850 EVO (120GB, 250GB, 500GB & 1TB) Review
by Kristian Vättö on December 8, 2014 10:00 AM ESTEndurance: 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 | ||||
| 120GB | 250GB | 500GB | 1TB | |
| 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).
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Kevin G - Monday, December 8, 2014 - link
They do seem a little low but we just got out of a major sale spree. During the Black Friday/Cyber Monday shopping fest the 480 GB Intel 730 was going for $200. I would have picked up one up myself at that price but they ran out of stock.HisDivineOrder - Wednesday, December 10, 2014 - link
You'd have been better served with the Sandisk Extreme Pro 480GB for $185.davolfman - Monday, December 8, 2014 - link
OCZ's firmware for the Barefoot3 series of chips the ARC100 uses has a less then stellar reputation. Things like unexpected power loss have been known to put it into a state of progressive corruption only recoverable by secure erase. There have been patches that claim to fix this on my Vector (that probably got applied to the ARC out the door), but I haven't seen anyone test if they're working.Oxford Guy - Wednesday, December 31, 2014 - link
Up to its old tricks, then.Kristian Vättö - Tuesday, December 9, 2014 - link
As listed on the table, the prices were taken on December 7 and were accurate at the time.sheh - Monday, December 8, 2014 - link
Can anyone explain the large discrepancy (not only in this case) in sequential speed between Iometer and AS-SSD?Kristian Vättö - Tuesday, December 9, 2014 - link
It's because of TurboWrite. Iometer is a time based tool and the sequential tests are run for one minute, which means that the TurboWrite buffer will be filled and thus the performance goes down as data is written to the TLC array. AS-SSD, on the other hand, only writes a gigabyte of data so it all gets written to the fast SLC cache.sheh - Friday, December 12, 2014 - link
Thanks. I'll have to reread older reviews, but I think there's a similar behavior also on other drives that do not have a fast temporary buffer?maecenas - Monday, December 8, 2014 - link
I saw the 840 EVO 500gb going for $180 over the black Friday - cyber Monday period. It'll interesting to see if Samsung keep the 840 EVO on the market as a the low end, so the 850 EVO can fill the mid-range portion of the market while the 850 Pro serves the high end.Laststop311 - Monday, December 8, 2014 - link
Prices are kinda crappy. Why go with an 850 evo when u can spend 20-30 dollars more and get an 850 pro?