[CentOS] DegradedArray message

[Keith Keller]

On 2014-12-03, David McGuffey <davidmcguffey at verizion.net> wrote:
>
> Appears to me that device 0 (/dev/dm-2) on md0 has been removed because
> of problems.

That looks about right.  There may be more error messages in your system
logs (e.g., /var/log/messages, dmesg), which might tell you more about
the nature of the failure.

> This is my first encounter with a raid failure. I suspect I should
> replace disk 0 and let the raid rebuild itself.
>
> Seeking guidance and a good source for the procedures.

The linux RAID wiki is often a good (though sometimes dated) resource.

https://raid.wiki.kernel.org/index.php/Reconstruction

If you wish to attempt a hot swap, make *sure* you pull the correct
device!  If you're not sure, or not sure your system even supports it,
it's safer to power down to do the swap.  You should verify which drive
has failed before shutting down, though this will be less catastrophic
if you pick the wrong one.

As long as you are careful, reconstructing a degraded RAID is usually
pretty straightforward.

--keith

-- 
kkeller at wombat.san-francisco.ca.us