Endurance

Samsung isn't quoting any specific TB written values for how long it expects the EVO to last, although the drive comes with a 3 year warranty. Samsung doesn't explicitly expose total NAND writes in its SMART details but we do get a wear level indicator (SMART attribute 177). The wear level indicator starts at 100 and decreases linearly down to 1 from what I can tell. At 1 the drive will have exceeded all of its rated p/e cycles, but in reality the drive's total endurance can significantly exceed that value.

Kristian calculated around 1000 p/e cycles using the wear level indicator on his 840 sample last year or roughly 242TB of writes, but we've seen reports of much more than that (e.g. this XtremeSystems user who saw around 432TB of writes to a 120GB SSD 840 before it died). I used Kristian's method of mapping sequential writes to the wear level indicator to determine the rated number of p/e cycles on my 120GB EVO sample:

Samsung SSD 840 EVO Endurance Estimation
  Samsung SSD EVO 120GB
Total Sequential Writes 4338.98 GiB
Wear Level Counter Decrease -3 (raw value = 35)
Estimated Total Writes 144632.81 GiB
Estimated Rated P/E Cycles 1129 cycles

Using the 1129 cycle estimate (which is an improvement compared to last year's 840 sample), I put together the table below to put any fears of endurance to rest. I even upped the total NAND writes per day to 50 GiB just to be a bit more aggressive than the typically quoted 10 - 30 GiB for consumer workloads:

Samsung SSD 840 EVO TurboWrite Buffer Size vs. Capacity
  120GB 250GB 500GB 750GB 1TB
NAND Capacity 128 GiB 256 GiB 512 GiB 768 GiB 1024 GiB
NAND Writes per Day 50 GiB 50 GiB 50 GiB 50 GiB 50 GiB
Days per P/E Cycle 2.56 5.12 10.24 15.36 20.48
Estimated P/E Cycles 1129 1129 1129 1129 1129
Estimated Lifespan in Days 2890 5780 11560 17341 23121
Estimated Lifespan in Years 7.91 15.83 31.67 47.51 63.34
Estimated Lifespan @ 100 GiB of Writes per Day 3.95 7.91 15.83 23.75 31.67

Endurance scales linearly with NAND capacity, and the worst case scenario at 50 GiB of writes per day is just under 8 years of constant write endurance. Keep in mind that this is assuming a write amplification of 1, if you're doing 50 GiB of 4KB random writes you'll blow through this a lot sooner. For a client system however you're probably looking at something much lower than 50 GiB per day of total writes to NAND, random IO included.

I also threw in a line of lifespan estimates at 100 GiB of writes per day. It's only in this configuration that we see the 120GB drive drop below 4 years of endurance, again based on a conservative p/e estimate. Even with 100 GiB of NAND writes per day, once you get beyond the 250GB EVO we're back into absolutely ridiculous endurance estimates.

Keep in mind that all of this is based on 1129 p/e cycles, which is likely less than half of what the practical p/e cycle limit on Samsung's 19nm TLC NAND. To go ahead and double those numbers and then you're probably looking at reality. Endurance isn't a concern for client systems using the 840 EVO.

Inside the Drives & Spare Area TurboWrite: MLC Performance on a TLC Drive
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  • B0GiE-uk- - Thursday, July 25, 2013 - link

    Seeing as this drive is similar to the 840 basic, it will be interesting to see the performance of the 840 Pro with the rapid software enabled. Has the potential to be faster than the EVO. I have heard that the rapid software will be backwards compatible. Reply
  • sheh - Thursday, July 25, 2013 - link

    Caching speed is based on RAM, flushing speed on drive. I don't think there will be any surprises. Reply
  • Heavensrevenge - Thursday, July 25, 2013 - link

    Finally were seeing transition to RAM caches, it's nice a RAM disk is being utilized and I hope the trend continues so that HDD/SDD can actually be taken out of the storage hierarchy for the OS & operating memory and have EVERYTHING reside in a non-volatile RAM space together for CRAZY increases in perf since HDD's in a way are a side-effect of old memory's being so small there had to be a drive backing the RAM. But of course we need traditional storage for actual storage purposes afterwards. But I'll hope for a migration of RAM towards a similarly fast combination of RAM+Drive being the main root drive built right onto the motherboards in a stick-like way within 10 years to cause a nice little computing revolution via re-architecting the classical storage hierarchy that's now, I believe, is quite possible and reasonable. Reply
  • DanNeely - Thursday, July 25, 2013 - link

    Modern OSes have been doing ram cache for years. Samsung is able to "cheat" with rapid because they've got a much better view of what the drive is doing internally to optimize for it (even if the data isn't normally exposed via standard APIs). Eventually OS authors will catch up and have SSD optimized caches instead of HDD optimized ones and it will again be a moot point. Reply
  • Jaybus - Thursday, July 25, 2013 - link

    Yes. It is doing the same thing as the O/S cache, but using a different algorithm to decide which blocks to cache, one that is tailored to SSD. So the O/S is very likely to adapt something similar in future.

    What is more interesting is TurboWrite. If you consider the on board DRAM a L1 cache, then TW implements a more-or-less L2 cache in NAND by using some of the NAND array in SLC mode instead of TLC mode. In addition to greater endurance, SLC mode allows much faster P/E cycles than TLC (or MLC). And unlike the DRAM cache, the SLC-mode NAND cache is not susceptible to power failure data loss. It still is not nearly as fast as DRAM, so the L1 DRAM cache is still needed. Encryption would kill performance without DRAM. But because data can be moved from DRAM cache to SLC cache more quickly, it frees up DRAM at a faster rate and increases throughput. So unless writing an awfully lot of data continuously, you essentially get SLC performance from a TLC drive. That is the EVO (lutionary) thing about this drive, much more so than RAPID software.
    Reply
  • Heavensrevenge - Thursday, July 25, 2013 - link

    Heh yes of course, I mean removing the "hard drive/solid state drive" out of the storage hierarchy completely and putting all OS and cache data into non-volatile silicon where the ram sits today, making all operations go as fast as ramdisk speed, not just have it there as a way to hide latency. like boot from the modules plugged directly into the motherboard and everything :) THATS what I'd love to see, 1-2GB/s 4K read & write speeds all-around not just for special use cases, All because the fab process is becoming small enough o fit the amount of data there we can actually re id f that part of the storage hierarchy if you know what I mean. Reply
  • Spunjji - Friday, July 26, 2013 - link

    I think there's always going to be a space for slower, more density-efficient storage in any sensible storage hierarchy. I think what you're looking forwards to is MRAM / PRAM, though. :) Reply
  • Heavensrevenge - Saturday, July 27, 2013 - link

    MRAM or any NVRAM is basically the concept I was wanting :) Thank you for the reference!!
    The day/year/decade that type of memory become our RAM & OS/Boot drive replacement in the storage hierarchy will be the one of the best times in modern computing history.
    Honestly all HDD/SDD manufactures should stop wasting their R&D on this type of crap even though SSD's are a wonderful "now" solution to the problem and I'll still recommend them for the time being.
    The sooner that type of memory is our primary 1st level storage directly addressable from the CPU the better our modern world of computing will become and begin evolving again.
    Reply
  • MrSpadge - Saturday, July 27, 2013 - link

    I don't think Samsung is doing anything better here, or working some SSD-magic. They're just being much more agressive with caching than Win dares to be. Reply
  • Touche - Thursday, July 25, 2013 - link

    I don't think your tests are representative of most people's usage, especially for these drives. TurboWrite should prove to be a much better asset for most, so the drive's performance is actually quite better than this review indicates. Reply

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