Discussion
A short story about data retention on modern SSDs and a word of warning about leaving them unpowered.
I recently helped a friend move his data to a new machine - and because of kerfuffle by his IT department - his new laptop arrived with a small SSD, so we had to leave some data behind until a larger one was available. I volunteered to move his Windows installation and old data on the new SSD as soon as it arrived, but life got in the way and 6 months went by before he showed up. 🧵 1/4
By sheer coincidence, I just wrote a minor lecture about flash a couple of days on VCFED:
https://forum.vcfed.org/index.php?threads/cf-card-vs-hdd.1258645/#post-1515080
The important bit is:
FLASH IS SIMPLY NOT A SUITABLE ARCHIVE MEDIUM!
@bsdphk there's one thing I'm curious about: do modern controllers periodically scrub data at rest or not? Because if they wait until the user reads the data some long-lived files that are seldomly accessed may deteriorate before they ever get touched.
When he did we had to pull some 500GB of data off this cheap TLC-based consumer drive with a Silicon Motion controller. This was mostly very large files and this drive could easily hit 500 MB/s read speed, so I didn't expect it to take too long. It took the entire day. The drive was struggling to maintain a 40 MB/s read speed, though it would occasionally burst to 500 MB/s. A quick look at the SMART data revealed what was causing this behavior: corrected read errors. 2/4
The drive was throwing thousands upon thousands of ECC read errors, most likely caused by the very little charge that remaind in the flash after 6 months without power and without being rewritten. I don't know if the low speed was because of a processing bottleneck in the controller when running the error-correction algorithm or at the analog level. Either way it seems that not losing any data in the process was a stroke of luck on our part. 3/4
So be wary when leaving an SSD off for a long time, especially TLC/QLC drives that are already pushing the limits of how much data can be crammed in a single flash page. The error margin might be eaten away quickly if the drive controller can't refresh the data. That's doubly true for enterprise drives which are meant to be powered 24/7. Regular hard-disks remain a better option for offline storage. 4/4
There are now tools which will refresh the data on SSD's to improve longevity and refresh data retention 🙂
Install bonfire.cafe
Get the full app experience
