On the Reliability of Automagic RAID

[Ben Scott]

On 1/12/06, Bill McGonigle <bill at bfccomputing.com> wrote:
>    /dev/md1 - /dev/hda4 - ext3 - /root (UH, OH)

  Was the RAID subsystem showing the md1 virtual device as a RAID-1
mirror with a failed member?  If so, check the logs.  I'd say the
system decided (likely due to the controller failure you mentioned)
that hdc4 had died, and was waiting for you to tell it, "Okay, problem
fixed, rebuild the mirror".

>    /dev/md2 - /dev/hdc4 - ext3 - not mounted (DOUBLE UH, OH)

  What was the RAID subsystem saying for the status of the md2 virtual
device?  Did the logs give any clue as to why the filesystem wasn't
mounted?

>    /dev/hda2 - swap (DANG IT!)

  One thing about RAID mirrors that can be confusing is that the
individual members are often indistinguishable from a simple, non-RAID
medium.  I suspect what happened here is that the auto-detect magic
saw hda2 as a valid swap device, and mounted it.  Then the RAID
subsystem saw hda2 as in use, and didn't activate the RAID member.

  This is one reason why, on servers, I usually specify filesystems
and swap explicitly by device, rather then using the LABEL= magic.

-- Ben