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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  • dgingeri - Friday, February 20, 2015 - link

    I replaced mine with an 850 Pro because of this issue, but I put the 840 EVO in an old laptop hoping it would still be good enough for that. Now I see it may not be. Reply
  • Alexvrb - Friday, February 20, 2015 - link

    Why? They sold a crapload and most of them are working fine. It's not a dreaded data corruption issue like a lot of entry-level SSDs have suffered, and it's correctable. I'd much rather have a hiccup like this that can be fixed without murdering your data, instead of a completely toast device like so many other budget SSDs.

    I've got an 840 Evo humming along nicely in one machine, and an 850 Evo in another. I only really go for Samsung and Crucial drives, myself, although I acknowledge that most of the Intel SSDs are very reliable too (if a bit costly).
    Reply
  • Samus - Friday, February 20, 2015 - link

    Fortunately I've only purchased 840 Pro's from Samsung which are amazing drives. All of my other drives are Intel 320, Intel 730 or crucial M550.

    What's funny though is even with the Evo 840 performance degradation, its still on par with an old X25-M or SSD 320...whats important to me is reliability first and foremost. I don't know if they are going to sacrifice data retention (long term data integrity) by shortening the read retry algorithms timeline. If they are... I would recommend you just deal with the peaks and valleys where there is slowdown until a tried and true fix is presented, because the drives are still very reliable IN FACTORY configuration before this, and future patches. But who knows, maybe it will just be over aggressive read retry algorithms after all... but I'm doubtful since they already tried to fix it by changing that.
    Reply
  • Alexvrb - Wednesday, February 25, 2015 - link

    I'd like to mention that in general I'm not a huge Samsung fanboy. I don't like their phones. I think many of their other consumer electronics are somewhat overrated. But I have had great luck with their SSDs. The Pros in particular ARE awesome, but for the money the Evo drives have always been hard to beat and nothing has really changed there. There's tons of problem-free systems out there with 840 Evos, and again since there's no data corruption I'm not stressing about it. I've seen one too many HDDs and badly-designed SSDs take a dump and eat all of your files to be freaked out by a repairable slow-down issue.

    Now if they had come out and said F you guys, buy our new 850 Evo, then I'd be outraged. But instead they continually work to make everyone happy, and their Magician software is both free and excellent (and they are dedicated to updating both the firmware with fixes as well as keeping Magician update).

    Anyway, I've had great luck with these older Evos and my newest 850 Evo is excellent. I picked up a 500GB unit so I finally feel like it isn't just a "boot drive" for me anymore. :D Now the only thing on my HDD is video!
    Reply
  • Notmyusualid - Saturday, February 21, 2015 - link

    Why? Because my two 840 Evos' performed SO bad, I had to break the RAID and use them individually.

    Or suffer much worse than a single-disk performance.
    Reply
  • TEAMSWITCHER - Sunday, February 22, 2015 - link

    "Well there's your problem." RAIDing together SSD's for more performance is a questionable practice. Reply
  • npz - Sunday, February 22, 2015 - link

    That is likely due to loosing TRIM in raid config. Reply
  • Alexvrb - Wednesday, February 25, 2015 - link

    Wow, that's silly. As the others have already said, any issues you're suffering are your own doing. Yikes man if one isn't fast enough RAID isn't going to help you! Just buy a single faster SSD instead of RAID, a Pro model for example, or even a high-end PCIe SSD if necessary. Reply
  • acsteitz - Thursday, August 27, 2015 - link

    I LOVE RAID 0. It does for data what Raid (insecticide) does for bugs, it kills it dead. (Old ad for Raid "Raid, it kills bugs dead.") In this day and age why anyone uses RAID 0 by itself is beyond me. If ANY drive in RAID 0 fails, you lose it ALL. Why would you double your chances of losing all your data for a not-noticeable-by-humans speed increase? Reply
  • Notmyusualid - Saturday, February 21, 2015 - link

    and me - x2 Reply

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