Bug#422554: Suggestion

[Bas van Schaik]

Did you check if hda and hdc got swapped by accident? I once had a
mainboard which had some awful bug: it swapped controllers after a
warm-boot (i.e. reboot). Controllers were somehow presented in another
sequence and Debian detected them the other way around. So: hda became
hdc, hdc became hda.

However, mdadm does (AFAIK) not make assumptions about device names, but
makes it's decisions based on the UUID and an event counter of an array.
In any respect, you're situation is very confusing and the last thing a
server administrator wants. Imagine a mailserver storing mail on an
outdated disk after a reboot: it'll directly outdate the other disk too!