Some 840 EVOs still vulnerable to read speed slowdowns


Patched drives exhibit problems with old data
— 2:22 PM on January 26, 2015

Last year, users discovered a problem with Samsung's 840 EVO SSD that caused dramatic slowdowns when reading older data. Samsung attributed the issue to an algorithmic error in the management routine that tracks the status of cells over time. A firmware fix and accompanying Performance Restoration utility were issued in October, and they seemed to do the trick. However, new evidence suggests that the problem persists.

A couple of TR readers (thanks Horia and Richard) pointed me to recent entries in the original Overclock.net thread complaining of slow read performance. Those reports come from drives running the supposedly fixed EXT0CB6Q firmware, and they prompted me to test an EVO I've been saving for just such an occasion. The results don't bode well for the TLC drive.

When the initial fix was issued, I patched our 840 EVO 250GB SSD and then filled it with a mix of movies, MP3s, images, and other files. That drive spent more than three months on the shelf before being called up for a round of read speed tests. Here's HD Tach's assessment:

35MB/s on a modern SSD? Yeah, that ain't right.

Next, I ran SSD Read Speed Tester, which tabulates read speeds based on the age of the files. This benchmark indicates that everything on the drive was almost 15 weeks old when the test was run.

The average here is 54MB/s, with some files reading at well over 100MB/s. That's faster than in HD Tach, but it's still a far cry from what the drive can do with fresh data.

Slow read speeds didn't just afflict targeted benchmarks, either. Transfer rates were extremely slow when I copied the EVO's contents to a secondary SSD in the same system. I then formatted the EVO, loaded it with the original data, and ran the same tests again.

That's more like it. The drive averages 430MB/s in HD Tach, a 12X increase. The EVO is about 10X faster according to SSD Read Speed Tester, which reports a 529MB/s average.

SSDs typically aren't left unpowered for months at a time, so it's possible that hiatus contributed to the slow read speeds exhibited by our sample. However, the other recent reports of read slowdowns come from drives that have been in service since the patch was applied. The issue doesn't appear to be confined to unused drives.

Bruno, our resident coder, has an 840 EVO in his personal machine. He agreed to run a few tests for me, and his drive isn't substantially slower to access older files. But NTFS compression was recently enabled for much of the drive's contents, so I'm hesitant to draw any conclusions based on those results. Compressing the data should effectively refresh the contents of the NAND cells even if there's no change in the stated age of the files.

We've notified Samsung of our findings and are awaiting an official comment from the company. In the meantime, I'm curious if any TR readers have experienced similar slowdowns. Have any of you noticed any read speed issues with patched 840 EVO SSDs?

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Tags: Storage