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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  • donawalt - Saturday, February 21, 2015 - link

    My performance has degraded on certain parts of the disk too
    https://dl.dropboxusercontent.com/u/56053396/test1...
    Reply
  • 3DoubleD - Sunday, February 22, 2015 - link

    I have degredation on at least one of my drives at this point. (FYI, I'm running on SATA2) https://www.dropbox.com/s/1b2s533spbagatc/HDTune-2...

    I need to check the rest now...

    This is unacceptable. I have three 840 EVOs and at least two family members with one drive each. Following Anandtech's glowing review and in combination with the aggressive pricing of this drive, it seemed like the SSD to buy. But performance like what I'm seeing is completely unacceptable. Large parts of my drive are writing at ~50 MB/s. Samsung really needs to fix this, either by issuing a fix that will work or by replacing everyone's drives.
    Reply
  • 3DoubleD - Tuesday, February 24, 2015 - link

    I've tested my other 250GB drive in my laptop https://onedrive.live.com/redir?resid=5005B9DD0DF2... This one appears consistent, but strangely only hits ~300MB/s across the whole drive with HD Tune (running on SATA3). Running the Samsung test yields sequential read speeds of ~520MB/s, so that result in itself is a bit confusing. However, I can live with consistent 300MB/s access. My other drive dropping as low as 8.8 MB/s has completely unacceptable performance. Reply
  • Achaios - Saturday, February 21, 2015 - link

    My 840 Evo's 500 GB performance has NOT deteriorated since applying the fix back in January. I use it everyday as my OS and games drive.

    http://i.imgur.com/ApsTUOZ.jpg
    Reply
  • Solid State Brain - Saturday, February 21, 2015 - link

    That benchmark isn't going to show if your SSD is affected by performance deterioration on old data. You have to use something like HDTach or HDTune with a block size set to a rather high value (in the several megabytes range). These programs will test all the logical blocks of the drive sequentially, bypassing the file system, regardless if these blocks actually contain data or not. On correctly working SSDs, sequential read speed should be constant from the start to the end of the user addressable space, regardless of the data contained and their age. Reply
  • michal1980 - Saturday, February 21, 2015 - link

    so Samsung is now basically OC their SSD drives to get them out the door, then patching them later. When will a tech site call them out for this? Reply
  • Yongsta - Saturday, February 21, 2015 - link

    My drive: http://i.imgur.com/1Ubz1Ad.jpg

    Bought it about a year ago, in October I had speeds as low as 250 MB/s but after the patch it went back up to 350 MB/s - 400 MB/s range. It doesn't appear to be as bad some people but I still want it to be better. I have about 9.10 TB written according to Samsung Magician, I think there might be a bug with the program because all I do is browse the web on this drive and Windows is installed on here (I use a ram drive for browser cache) and my programs / games / movies are all stored on a separate SSD but for some reason my total bytes written sometimes goes up around 0.5 TB a day when I used the computer for only a few hours and browsed a few websites. Anyone else experience this bug?
    Reply
  • critter13 - Saturday, February 21, 2015 - link

    Has anyone been able to implement the fix on a mac? I simply cannot get it to work. Reply
  • Achaios - Saturday, February 21, 2015 - link

    Here's my HT TACH result:

    http://i.imgur.com/otQfe9o.jpg

    I ran it will playing World Of Warcraft. Lowest speed was 375 MB/Sec, and avg spd abt 430 MB/s. presumably, if I ran the test with no programs running I'd get even better results.

    My drive appears to be okay. I applied Samsung's fix on January 7, 2015. You can check my Samsung Magician's results on my previous comment.
    Reply
  • mercutio - Saturday, February 21, 2015 - link

    still having 840 non evo issues, tried contacting samsung who were no help.

    now days you can get cheap crucial m4 recertified on crucial's web site which are still faster than 840/840evo for read speeds.
    Reply

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