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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  • tincmulc - Thursday, July 25, 2013 - link

    How is rapid any better from SuperCache or FancyCache? Not only do they do the same thing, but can also be configured to use more ram or use os invisble memory (32 bit os with more than 3GB of ram) and they work for any drive, even HDDs. Reply
  • spazoid - Thursday, July 25, 2013 - link

    It's free. Free is better. Reply
  • jhh - Thursday, July 25, 2013 - link

    Are there any latency measurements in milliseconds as opposed to IOPS? With IOPS, the drive may be queuing rquests, making it difficult to translate IOPS to milliseconds per request. Reply
  • Kibbles - Thursday, July 25, 2013 - link

    If I write 1gb/day on average to my SSD, since media files go on my home server, this drive would last me 395 years LOL! Reply
  • sheh - Thursday, July 25, 2013 - link

    Anand, would you consider writing an article on the other aspect of endurance: data retention time? With TLC entering the fray it's starting to get even more worrying.

    It'd be interesting to know how retention time changes throughout a drive's life, trends in the last few years, differences between manufacturers, the effect of the JEDEC standard, whether there's any idle-time refreshing for old written cells, etc.

    And an idea: I'd like to see drives where you can configure whether to use the drive as SLC/MLC/TLC. Switch to SLC for reliability/performance, TLC for capacity.
    Reply
  • MrSpadge - Saturday, July 27, 2013 - link

    "And an idea: I'd like to see drives where you can configure whether to use the drive as SLC/MLC/TLC. Switch to SLC for reliability/performance, TLC for capacity."

    Or a drive which switches blocks from TLC operation to MLC as it runs out of writes cycles. And finally to SLC.. at which point in time it should last pretty much infinitely.
    Reply
  • mgl888 - Thursday, July 25, 2013 - link

    Great article.
    Does RAPID require that you install a separate driver or does it just work automatically out of the box? What's the support like for Linux?
    Reply
  • bobbozzo - Friday, July 26, 2013 - link

    It's a driver, for Windows. Reply
  • TheinsanegamerN - Saturday, July 27, 2013 - link

    and i dont think that rapid has a reason to be on linux. linux is already much better with ssd writes than windows. Reply
  • chizow - Thursday, July 25, 2013 - link

    Minor spelling correction: http://www.anandtech.com/show/7173/samsung-ssd-840...

    "counterfit" should be "counterfeit"
    Reply

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