[breput]

The spinrite[0] user group has noticed some of these effects, even on in-service drives.

The theory is that operating system files, which rarely change, are written and almost never re-written. So the charges begin to decay over time and while they might not be unreadable, reads for these blocks require additional error correction, which reduces performance.

There have been a significant number of (anecdotal) reports that a full rewrite of the drive, which does put wear on the cells, greatly increases the overall performance. I haven't personally experienced this yet, but I do think a "every other year" refresh of data on SSDs makes sense.

[0] https://www.grc.com/sr/spinrite.htm

[2WSSd-JzVM]

If full rewrite helps doesn't it sound like TRIM implementation in SSDs is buggy or insufficient? Or internal cell wear-maps aren't detailed enough. Anyway plenty ways it can go wrong, SSD firmware had also plenty of high profile bugs, including total bricking.

[londons_explore]

There are lots of other potential causes for the same effect...

Eg. Data structures used for page mapping getting fragmented and therefore to access a single page written a long time ago requires checking hundreds of versions of mapping tables.