Over the last month there has been some concern over the read performance of Samsung’s 840 EVO drives, and whether after Samsung’s previous performance fix, that these same drivers are starting to regress in performance once again. Since then we have been pressuring Samsung for additional information on the issue and a response, and this afternoon Samsung has finally issued a statement on the matter.

In October, Samsung released a tool to address a slowdown in 840 EVO Sequential Read speeds reported by a small number of users after not using their drive for an extended period of time. This tool effectively and immediately returned the drive’s performance to normal levels. We understand that some users are experiencing the slowdown again. While we continue to look into the issue, Samsung will release an updated version of the Samsung SSD Magician software in March that will include a performance restoration tool.

As a reminder, the original 840 EVO performance degradation issue was a result of a combination of NAND cell charge decay and NAND management algorithm issues. While NAND cell charge decay is a normal part of NAND operation, it was something Samsung’s more complex TLC NAND was more sensitive to. Meanwhile Samsung’s algorithms, when faced with this decay, erroneously went into an aggressive read-retry state, which is ultimately what lead to the drop in read performance. Samsung’s fix in turn addressed their NAND management algorithm, and at least at the time was thought to be a permanent fix for the issue.

These more recent performance issues and now Samsung’s statement make it clear that the issue is unfortunately not as fixed as Samsung initially thought it would be. At this point Samsung isn’t saying what the root cause of this latest issue is, but it’s likely that this is a continuation of the original issue. In any case the upshot is that Samsung believes the issue can be corrected, however given the last fix it’s not clear whether this next fix will be any more a permanent fix than the last one.

Source: Samsung (via email)

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  • kgh00007 - Friday, February 20, 2015 - link

    My 120GB 840 EVO went back up to 350MB/s across the whole drive after applying the fix on the 15th of October last year.
    Now the speed has dropped to below 100MB/s (and even below 50MB/s in places) across 50% of the drive.

    I'm shopping for a new SSD for a new laptop and I can't bring myself to buy the 850 EVO because I don't trust it.

    I too would like to have this drive replaced with a drive that performs to the stated specification. My laptop now takes just as long to start up from shutdown with the 840 EVO as it did with the HDD.

    The media were all over these drives quoting the best speeds and awesome service times, but The reality is that these drives perform terribly in real life!!!
    Reply
  • ZeDestructor - Saturday, February 21, 2015 - link

    Get a Crucial MX100 or MX200 then. Somewhat slower than the 850 EVO, but reliable... Reply
  • kgh00007 - Saturday, February 21, 2015 - link

    Yeah cheers! I've had a Crucial M500 240GB for just as long as the 840 EVO. While it's a "slower" SSD, it's performance has remained constant the whole time and feels like the faster SSD! Reply
  • Pissedoffyouth - Monday, February 23, 2015 - link

    Yeah the m500msata is a lovely drive. Reply
  • Impulses - Saturday, February 21, 2015 - link

    Was there ever a fix for the original 840 non-EVO? Reply
  • Solid State Brain - Saturday, February 21, 2015 - link

    I've got two and I agree it would be nice to know if non-EVO 840 will ever be fixed. Reply
  • Jumangi - Saturday, February 21, 2015 - link

    They just need to bite the bullet and offer a recall/replacement for owners. Reply
  • FriendlyUser - Saturday, February 21, 2015 - link

    Hm, back to Plextor and Intel drives, I guess. Samsung is cheap, but not as reliable as I thought. Reply
  • Murloc - Saturday, February 21, 2015 - link

    I found out about this a few days ago and ran the test: my slowest speed is 0.7 MB/s.

    Yet I haven't noticed any slowdown, despite not having rewritten many of the files I read often.
    Reply
  • wavetrex - Saturday, February 21, 2015 - link

    I just run HDTach myself, noticed the big dips.. run the performance recovery, they are gone. I only have the SSD since last week and already these problems...
    Huh... wonder how long until I have to run the software again. Starting to regret the choice in buying it...
    Reply

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