Some of Samsung’s TLC SSDs are slow to read old data

Samsung has deployed three-bit TLC NAND in two generations of solid-state drives: the 840 Series and the 840 EVO. The value-oriented drives have been very popular, but they seem to have a problem. Scores of owners are reporting that older files have substantially slower read speeds than newer ones. The problem is detailed in several Reddit and forum threads, including this epic one over at Overclock.net. It's on Samsung's radar, as well. The company provided the following statement when we inquired about the issue:

Samsung recognizes the seriousness of any potential degradation of read performance on old data. We are testing and validating the circumstances that potentially cause this performance drop and will work diligently to resolve the issue.

Online reports suggest the problem only manifests in files that are several months old. Some users are reporting read rates as low as ~20MB/s for data that should read at 10-20X that speed. Drives may not have to be powered on for read performance to suffer, either. I've seen at least one post complaining about slow reads on a drive that was unplugged and untouched for months after being filled with data.

Full performance can apparently be restored by rewriting the affected files or defragging the drive. Defragmentation does plenty of rewriting, but it's typically not recommended for SSDs, which have limited write endurance and are unaffected by file fragmentation.

There are a couple of theories about the cause. One pins the blame on the background garbage-collection and wear-leveling algorithms that shuffle data around on the drive. SSDs achieve peak performance by accessing data over multiple NAND channels simultaneously, but the data must be distributed across multiple physical flash dies to take advantage of that parallelism.

The other theory involves a change in cell voltages over time. Flash memory writes data by trapping electrons inside a floating gate. Electrons can leak out of the cell over time, though, and cells are prone to interference from the activity of their neighbors. TLC NAND is especially sensitive to voltage changes because it must differentiate between more possible values within each cell. Error correction routines are supposed to compensate, but the amount of work required to read older data accurately could be responsible for the slower performance observed on the 840 Series and 840 EVO.

We have several of the affected drives in the lab, but due to the order in which we benchmark SSDs, none of them have any old data on them. We took a shot at simulating the problem over the weekend by filling an 840 Series and 840 EVO 250GB with 10GB of static data. We read those files, hammered the drives for 24 hours with our IOMeter "workstation" access pattern, and read the original data again.

Read performance dropped on both drives, but only by about 20MB/s. The data were only a couple days old, which may explain why read speeds didn't drop further.

In any case, the issue appears to be very real. Let's hope Samsung can address it with a firmware update—one that hopefully doesn't require wiping the drive. In the meantime, users at least seem to be able to access all their info, even if they have to wait for it.

Comments closed
    • wiak
    • 5 years ago

    Guys
    how do you test read on older files? what application do you use?
    i have a 840 in a drawer somewhere, been there for months
    i hope there is some data i left on it still

    • thorz
    • 5 years ago

    I have an 840 Evo 750GB on this Macbook Pro.
    I hope that when they release a fix they also remember to make it available to us that are not in Windows.

      • wiak
      • 5 years ago

      you can always run the bootable CD/USB…
      or do you PC (intel x86-64 cpu) powered MAC dont boot cds or usb?

    • Musafir_86
    • 5 years ago

    -So, how about those TLC NANDs in Galaxy smartphones and tablets? Will they suffer the same fate? 🙁

      • Vaughn
      • 5 years ago

      I think how you connect to the phone/tablet will be a bigger issue than the NAND speed.

      USB 2/3
      Wifi N/G

      Not to mention the NAND in cell phones is usually lower grade than what you get in an SSD.

    • Scolasticus
    • 5 years ago

    Interesting. I did a pretty non-scientific test on my laptop. I have a 250GB 840 Series Samsung SSD that I purchased about a year ago, and copied files on to it from a mechanical HD at that time. There’s a few old movie files that I haven’t looked at since I copied them over. I have a smaller system SSD, then the Samsung SSD as a data drive. The first time copying 420MB movie file from the Samsung SSD to the system SSD gives transfer rates of about 70MB/sec in windows explorer.
    If I copy the file back to another location on the Samsung SSD, delete the file on the system SSD, reboot the laptop and copy again, I get 171MB/sec. Not being particularly technical I don’t know whether there is another explanation for this, but it does seem like quite a difference.

    NB – The system drive is not a particularly great SSD, which is why it is topping out at 171MB/s write.

    • f0d
    • 5 years ago

    im guessing this happens with new firmware? because mine had no speed issues at all with the release firmware that i had on it since the release of the 840 evo

    funnily enough i thought i would update the firmware about a week ago before i saw any news of this problem – i really wish i diddnt do it now (i usually go by the mantra of “if it aint broke dont fix it”)

    • ozzuneoj
    • 5 years ago

    I sure hope they are able to fix this. I’m actually quite happy with my 256Gb EVO, but I have noticed once in a while that things seem to take longer than they should on a reasonably quick laptop (i5 3210M, 6Gb DDR3).

    If it gets worse I’ll be pretty irritated. My relatively ancient 64Gb Crucial C300 in my desktop is still plugging along as smooth as it was the first day I bought it (for $150… and that was a bargain).

    • meerkt
    • 5 years ago

    Another theory: limited retention rearing its head? And so more error correction, and rewrites, need to kick in.

    • UnfriendlyFire
    • 5 years ago

    To the guy who stated that there’s nothing wrong with a slow SSD, tell me what’s the purpose of buying a more expensive SSD that has lower performance than a cheaper one (Crucial MX100, M500) that has higher performance.

    It’s like a laptop manufacturer selling a laptop with an i7 and GTX 860M. Then not informing the consumers that due to issues with the power delivery and cooling system, the i7 throttles to 800 mhz and the GTX 860M is stuck at idle clock rates when operating temp exceeds 60C.

    • tootercomputer
    • 5 years ago

    I have a 128G 840 Evo on my main system at home, Win 8.1Plus, it’s my OS drive. I’ll have to check this out a bit.

    Two questions, does this affecting accessing files from another drive? Doesn’t sound like it.
    Also, anyone know if the Samsung software has bee ruled out, the stuff that comes with the drive? Not sure if that would affect anything, but you never know.

    I’ve had tjos drive for some months now and can’t say I’ve noticed any problems, but I mostly access files off my mechanical storage drive.

      • meerkt
      • 5 years ago

      Why would it affect other drives?

      And I wouldn’t think it’s a software issue.

    • cygnus1
    • 5 years ago

    This is my anecdotal experience but the performance hit on my EVO was pretty dramatic. It was very erratic with the most significant symptom being the very high latency, not necessarily the slow speed. Task manager was showing thousands of ms of latency reading old files on the drive. The end result of course was low throughput but the latency caused other severe issues. In my case it was in the pagefile. The latency spikes hitting old files caused calls to the pagefile to time out which caused all sorts of issues. Disabling the pagefile seemed to fix that issue. Then after setting up a daily image based backup the performance of my drive seems to have improved. After that I was able to turn the pagefile back on and not have further issues. It’s still not running as fast as it was a couple months ago. I would likely have to secure erase the drive and then restore the latest backup to get it back to normal speed.

    • someuid
    • 5 years ago

    I thought this was old news. Steve Gibson covered it several weeks ago, maybe two or three months ago, that SSD cells will lose a bit of charge over time and the cells have to be read and written again to refresh the charge. He was particularly happy because he thought SSDs would mean the end of a need for SpinRite and that was not proving the case. I wish I remembered which episode of Security Now it was in which he discussed it.

    Edit:
    A quick search brings up episodes 373 and 387 where he discusses SpinRite and SSDs.

    • GTVic
    • 5 years ago

    Maybe cutting costs by having the drive upload old data to the cloud wasn’t a great idea.

      • xeridea
      • 5 years ago

      If I could read from the cloud @ 20MB/s I wouldn’t be complaining….

        • UnfriendlyFire
        • 5 years ago

        Your ISP would’ve throttled your connection well before 10 MB/s (= 80 Mbps), at least if you’re living in the USA.

          • Waco
          • 5 years ago

          Missing the point much?

            • GTVic
            • 5 years ago

            Yes, plus trying to one-up someone else’s remark with sarcasm on another topic is in poor taste, ditto for the first reply, doubly so because it got more thumbs up.

    • Freon
    • 5 years ago

    Hmm, wonder if a Spinrite “surface refresh” will fix it. I’m guessing so.

    • PrincipalSkinner
    • 5 years ago

    And I even felt silly when I bought Pro over EVO. Hah!

      • wiak
      • 5 years ago

      i think Samsung’s good track record had so go sometime, i guess its time, hopefully the fix is good

      FYI: owner of 840, 840 EVO and 840 PRO here

    • hieu.noob
    • 5 years ago

    Not sure where to place the blame, but my OS crapped out on me and required a format as it was totally inaccessible, with a 120GB Evo as the OS drive…

      • brucethemoose
      • 5 years ago

      The problem is obvious… It was the NSA.

    • DancinJack
    • 5 years ago

    I don’t know why people are making such a big deal about this. Yes, there is a bug. Yes, Samsung has acknowledged it. Yes, they are working on a fix. As long as people don’t actually lose data I don’t see much of a reason to complain. Meh.

      • stdRaichu
      • 5 years ago

      Same reason people got upset when the crucial M4 fell over after 5000 hours – it’s a “that’s not supposed to happen” problem in an otherwise great drive that should have been spotted by the manufacturers earlier so that a fix could be started on ahead of the issue gaining widespread visibility.

      Hopefully this issue will see samsung do better long-term testing.

      • wierdo
      • 5 years ago

      Many people are buying SSDs to leave HDD performance behind, so I would assume people would be a bit annoyed to see 20mb/s performance out of their investment.

      That would be one guess.

        • DancinJack
        • 5 years ago

        I get that, but what I am saying is that there is no guarantee the drive will work that fast and Samsung has already said they are fixing it. I doubt it will take long. Let’s just be patient folks.

        • UnfriendlyFire
        • 5 years ago

        Notebookcheck downgraded a laptop’s ratings after learning that some of the models were using an extremely slow SSD instead of the SSD that the review website tested.

        The manufacturer used two different SSD models for the same laptop model, one had acceptable performance, the other had performance WORSE than 7200 RPM HDDs in random/sequential performance.

      • not@home
      • 5 years ago

      I’m going to complain. I do not have one of those drives and I want one.

        • Meadows
        • 5 years ago

        Pick the 840 Pro instead.

      • ddarko
      • 5 years ago

      If people hadn’t complained, how would Samsung know about it? Magic? Telepathy?

      And of course there’s an implicit promise that the drive shouldn’t be reading data so slowly – read rates like this are far outside the advertised parameters of the drive. No, Samsung doesn’t “guarantee” that every read operation will be 200MB/s or above. But “age of data” has never been one of the factors consumers have been told or informed could affect SSD drive performance. Fortunately for people who have this drive, Samsung isn’t taken your position that “we didn’t guarantee speeds” and it acknowledged that data age shouldn’t trigger such a drastic drop and the drop falls well outside the normal and expected leeway.

      And while you may be laid back about it, there’s no guarantee at this point that Samsung can fix it. Until Samsung figures what’s behind this, folks are worried about the integrity of their data and the durability of the drive they bought. It’s perfectly understandable why people are concerned. They’re not overreacting.

        • cygnus1
        • 5 years ago

        Exactly this.

        **the rest of this is my conjecture, I am not a flash design engineer or a lawyer**

        Given the nature of flash, I’m very much worried the fix for this will be to force old cells to be re-written more aggressively than Samsung had initially designed for, thus reducing the lifespan of the drive.

        I’m guessing if that happens, Samsung may be the target of a massive class action lawsuit. I think Samsung’s best bet, if that durability reduction is indeed the fix, would be to basically do a recall and to pre-emptively start a drive replacement program to a different model. They’ve sold a lot of these TLC based drives which means a very large class for that lawsuit, so I’m thinking that recall would likely be cheaper than litigating.

      • albundy
      • 5 years ago

      I sure as hell do. paying a premium on a product that not only does not deliver, but degradates tells me it was rushed out to make as much profit as possible with very little testing, while leaving the consumer hanging. Oh yeah, i demand my money back for a faulty product! what’s really surprising is that there’s no class action against them.

      • Meadows
      • 5 years ago

      Dude. It makes those SSDs five times slower than an HDD.

      • Krogoth
      • 5 years ago

      Just more silly drama.

      This is nothing compared to earlier SSD issues where drives would lose data or suffer corruption.

    • Wildchild
    • 5 years ago

    Great! I finally just got an 840 Evo a few months ago D:

    • ronch
    • 5 years ago

    Of all the drives in the market, I had to get an EVO. Oh well. I should’ve waited for those AMD Radeon Solid State Drive[b<]s[/b<].

    • brucethemoose
    • 5 years ago

    A glitch in a Samsung SSD?

    Lies!!!

      • TwoEars
      • 5 years ago

      I was thinking the same thing! The sun has spots? Damn.

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