Samsung Bug in Evo 840 SSD

During the last couple of weeks, more and more reports have started to surface about problems with the Samsung 840 and Evo 840 drives. The trouble in question is extremely low speeds when reading old data, meaning data that has been written over a month ago. Freshly written files will have the same performance as the drive has advertised.

The biggest collection of information about this bug is over at the Overclock.net forums. The thread is close to 750 replies at the time of writing, and more are coming in all the time, and the thread itself started about a month ago. As more people get aware of the problem, more reports pop up all over Reddit and other user forums as well.

The HD Tach graph below illustrates the issues with these drives. The odd part for now, is that the bug only affects LBA’s that have old data associated with them. Freshly written data has the full speed. This explains very well how such a severe bug could have been hiding for so long. The good news is, it’s most likely a firmware issue and can be fixed with an simple update.

Anandtech has reached out to Samsung via phone and it seems they are both aware of it and working on a fix. Presumably the bug has been located. There’s sadly no ETA on a possible fix yet, but it’s great to see Samsung working hard to fix this issue. But then again, it is in their own interest to do so.

I am running a 1 TB Samsung Evo 840 in my personal system, so of course I had to test this out myself. I can verify that the bug is present on my drive as well. This could very well attribute to some of the lags and slow loading times I’ve been having when working with my PC. Doing a normal disk-to-disk copy of fresh data results in about 250 MB/s, which is normal for that folder. An old data copy however swings between 300 kb/s and 2.5 MB/s with peaks up to 6 MB/s. That’s not what I’d call SSD speeds.

Update September 25: Estimated time for a firmware update is set to October 15, we’ll keep you updated.

Thank you Anandtech for providing us with this information

Image courtesy of Anandtech.