During the last couple of weeks, numerous reports of Samsung SSD 840 and 840 EVO having low read performance have surfaced around the Internet. The most extensive one is probably a forum thread over at Overclock.net, which was started about month ago and currently has over 600 replies. For those who are not aware of the issue, there is a bug in the 840 EVO that causes the read performance of old blocks of data to drop dramatically like the HD Tach graph below illustrates. The odd part is that the bug only seems to affect LBAs that have old data (>1 month) associated with them because freshly written data will read at full speed, which also explains why the issue was not discovered until now. 

Source: @p_combe

I just got off the phone with Samsung and the good news is that they are aware of the problem and have presumably found the source of it. The engineers are now working on an updated firmware to fix the bug and as soon as the fix has been validated, the new firmware will be distributed to end-users. Unfortunately there is no ETA for the fix, but obviously it is in Samsung's best interest to provide it as soon as possible.

Update 9/27: Samsung just shed some light on the timeline and the fixed firmware is scheduled to be released to the public on October 15th.

I do not have any further details about the nature of the bug at this point, but we will be getting more details early next week, so stay tuned. It is a good sign that Samsung acknowledges the bug and that a fix is in the works, but for now I would advise against buying the 840 EVO until there is a resolution for the issue.

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  • sweeper765 - Friday, September 19, 2014 - link

    Thanks for writing about this. So far Samsung support (almost impossible to contact by the way) wasn't very helpful in responding to the user complaints, saying the bug didn't show up on their end and that users shouldn't test with an old bench like HDTach (ironically used in this article).

    Glad they acknowledge the issue and it is fixable.
  • JarredWalton - Friday, September 19, 2014 - link

    I think it's general practice at big businesses to deny the existence of a problem and try to avoid all culpability until a fix has been found. After all, if you admit there's a problem and you can't actually fix it, you've basically killed your product. Samsung publicly admitting there's a problem means they're probably done with the fix and are just running internal validation at this point. Guess we'll see what happens next week.
  • jay401 - Saturday, September 20, 2014 - link

    It's sad that's considered an acceptable practice these days. It sounds like the result of the "share value > customer service" attitude created by publicly-traded corporations.
  • semo - Saturday, September 20, 2014 - link

    Why support customers. They've got their money already! New customers get drawn in by the marketing machine and existing customers get distracted by script reading monkeys. As for disgruntled customers, we all know that one screwball can't make a difference.
  • Fergy - Monday, September 22, 2014 - link

    That is why you should force companies to by law give 5 years warranty. Maybe some components even more.
  • NikosD - Sunday, September 21, 2014 - link

    Congratulations to Anandtech.com and Kristian Vättö personally, who decided to expose this VERY SERIOUS BUG.

    For all us customers of 840 EVO, I think it's a milestone that Samsung after this "outing" of anandtech, at least acknowledges the bug and hopefully they will fix it.

    If they don't, they should be prepared for legal actions against them, in case they decide to not give us our money back.
  • jowdy - Friday, September 19, 2014 - link

    Hopefully people can now shut the hell up about this *still* amazing series of SSDs.

    Dismount off the Bandwagon, folks.
  • hojnikb - Friday, September 19, 2014 - link

    Yeah, my thoughs exactly.
    Even though its still a great ssd and for some time, it was the best value for money, it was slowly outrun by competition with similar performing drives at lower pricepoints. And all of them feature a more robust MLC flash (well sandisk is an exception now).
  • MacDude2112 - Friday, September 19, 2014 - link

    Anyone care to recommend specific alternatives, hopefully in a 500GB capacity? I'm open to suggestions.
  • hojnikb - Friday, September 19, 2014 - link


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