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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  • sepuko - Wednesday, October 15, 2014 - link

    Could "Anandtech" call these guys again and ask them what the h**l is going on and why is this update not released? Cause sure as h**l they are not moved by individual users, what do they care if I buy their products, if I do not represent a big corp. customer to suck up to I am irrelevant. I am running an 840 Evo 250G since February with the latest firmware. The performance is a disgrace. I have recommended against buying Samsung SSD in the past 6 months and will continue to do so until I see a change. I am working in a big enterprise software provider and we are looking for ways to improve performance. I was the first and only one to buy a Samsung. The performance of this SSD is laughable, why would they? Reply
  • Guyp16 - Wednesday, October 15, 2014 - link

    Looks like we aren't going to get this firmware download for Mac / Linux users today or for a while. From Samsungs download page - Dos version for MAC, Linux users Will be released on end of Oct. Shame on them. Reply
  • scunmmonk - Wednesday, October 29, 2014 - link

    http://www.samsung.com/global/business/semiconduct... - DOS Version for Linux, MAC OSX released ;-)

    Yeah I used the DOS Version Samsung EVO 840 Performance Restore ISO as I am using a EVO 840 1 TB in my Macbook with native only MAC OSX. It was 15 Minutes or so Performance + update to the firmware!!
    Reply
  • sdr - Wednesday, October 15, 2014 - link

    Windows version has been released and available for download from SAMSUNG.
    "Samsung SSD 840 EVO Performance Restoration Software"

    Can anyone with old data files upgrade and do a validation test.
    Reply
  • aaront - Wednesday, October 15, 2014 - link

    looks like the fix worked
    http://techreport.com/review/27212/samsung-840-evo...
    Reply
  • Chargerdude - Monday, October 27, 2014 - link

    My 840 EVO is nearly a year old but has not had heavy use in my HTPC and showed no symptoms. The repair tool worked with no problems. It took about a half hour to repair my 120 G drive. Reply

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