Update: In diesem Fall war es wohl ein Fehler im Linux-Kernel.

https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg1340177.html
» The bug affected raid0 and raid10 (but apparently not raid1) when TRIM was
» enabled. Apparently it's been around a while, it probably exists older
» debian releases but I have not checked.
»
» Also: as the blog June 16th update states, this bug was NOT related to
» queued TRIM as they didn't have that enabled, so probably unrelated to
» #790520.

Der im letzten Satz genannte Bug 790520 [debian.org] bezieht sich auf TRIM in Verbindung mit “native command queuing” [wikipedia.org]; dieses Problem besteht weiterhin.