There’s been word going around that Samsung’s 840 EVO solid-state drives have an issue where they become really, really slow to read if the data on it has been sitting around for a few months, and I can confirm this is the case as well.
The first half of the drive (which holds a fair amount of static data) was being read at around 30 MB/s, with newer data being read at almost 500 MB/s. That’s a pretty big difference. One thing to note (I didn’t take a screenshot for this) is that although the overall read speed was significantly affected, the read latency was only somewhat slower; only about 10-20 microseconds of extra latency.
To temporarily fix this (at least until Samsung releases a firmware update in the middle of October), I used Hard Disk Sentinel to read and rewrite all of the data on the SSD. Because this involves accessing data that is normally locked by Windows, I made a custom WinPE (a slimmed-down, portable version of Windows that’s used for installation and recovery) image with Hard Disk Sentinel inside it. This allowed me to boot outside of the normal Windows setup, and perform the Read+Write+Read test to refresh all of the data stored on the SSD. Note that this will impart a lot of write activity to the NAND flash in the SSD (hence a chance for increasing wear), but modern SSDs aren’t as delicate as people might think.
This took about 2 hours on my 250 GB SSD. Afterwards, another read test showed that the drive was working smoothly again.
Will I still buy a Samsung SSD? Absolutely. No data was lost and Samsung did the right thing by acknowledging the issue and also finding a way to fix it, as opposed to simply calling it a non-issue and sweeping it under the rug.