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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  • TEAMSWITCHER - Friday, September 19, 2014 - link

    Great...and I've been using the damn things as OS/App/boot drives. Samsung needs to get their shit together. I have a Samsung refrigerator with a broken ice maker (less than 2 years old) and a dishwasher that only works on one setting (purchased at the same time as the refrigerator.)

    Needless to say I have no confidence in the brand anymore.
  • danstek - Friday, September 19, 2014 - link

    To be fair, Samsung's home appliance division has nothing to do with Samsung semiconductors.
  • fallaha56 - Friday, September 19, 2014 - link

    i'm in the same spot bud -but at least now i understand why my system feels so slow lol
  • danstek - Friday, September 19, 2014 - link

    What about OEM versions of this drive?
  • Kristian Vättö - Friday, September 19, 2014 - link

    I should have a confirmation next week, but the OEM drives are very likely affected too since they share the same firmware architecture as the retail drives.
  • PCHardwareDude - Friday, September 19, 2014 - link

    Finally someone wrote about this huge issue. I'm amazed that it has taken the tech journalism world this long to bring this debilitating issue to light - especially after so many of them advocated these horrible horrible drives.
  • Beef Meister - Friday, September 19, 2014 - link

    It's funny, I thought I was experiencing IO slowdowns at some times, but dismissed it as my imagination, since all my frequently used/updated stuff worked well. But OUCH, it is actually a lot worse than I thought...... http://i.imgur.com/LnBG1Pq.jpg

    Some areas below 10Mb/s. Good thing I have backups! :/
  • fallaha56 - Friday, September 19, 2014 - link

    me too buddy -thought i was imagining things
  • MacDude2112 - Friday, September 19, 2014 - link

    I actually purchased this drive strictly for fast seek times and fast access to large amounts of small files that are never modified (aka streaming music samples for composition). I am VERY disappointed to hear of this problem, as it directly effects what I purchased the SSD to do! For anyone saying this isn't a big deal, I'm confused as to how they use HD's. Does no one access older files and want them to be accessed at the speeds they paid for when buying an SSD?

    Any other recommendations of an alternate SSD, or should I just wait and hope Samsung can fix this issue? I really hope they allow for easy updates for Macs as well as PC's!!
  • Coup27 - Friday, September 19, 2014 - link

    They do. Samsung release their updates via Windows software and .ISO files you can boot.

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