recovery problems, might be driver-related

["Stefan Hübner" <stefan.huebner@stud.tu-ilmenau.de>]

Hi Everybody,

I've recently come across some RAID-Recovery problem that were kind of
not-so-easy-to-understand.  I was trying to recover damaged RAID5s,
where one
disk died and another dropped out (most likely due to read error recovery
timeout / not reporting back while error recovery was active) during
resync with
a spare/new disk.  After taking double backups I tried to recreate the
raid with
the needed working disk images (to make the superblocks consistent).  During
that action mdadm told me that the last-dropped disk contained a valid ext3
filesystem and was obviously part of an md-array.

This happened with NAS-Devices from 2 different Vendors (namely Thecus and
Synology), which made me think it must be a md-raid thing.  Does md-raid
create
a filesystem after a disk dropped out?  Or may something in the system
happen to
cause this strange behaviour?

All in all: after recreating the raids the filesystem contained on it was
totally damaged (could not even be mounted).  fsck ran multiple days with
excessive data loss.

P.S.: the mdadm-lines to recreate the RAIDs were derived from mdadm -E -
outputs
of the original partitions, so I believe that it should have worked (on
other
recoveries I did before it also worked well).

Does anyone have an idea what is going on there?  Or may it have happened -
well, I don't want to say something that could get me sued.

All the best,
Stefan Hübner
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