[mdlug] "Device busy" errors and RAID setup issues

[Jeff Hanson]

On Fri, Nov 20, 2009 at 7:41 PM, David McMillan <skyefire at skyefire.org> wrote:
>        Well, I did that.  Successfully created /dev/md0.  /proc/mdstat showed
> /dev/md0 active and containing all of the hard drives except the one I'd
> left as "missing" in the initial setup.  I even put a label on it and
> created a filesystem on it.
>        Then I rebooted the server.  And now /dev/md0 is gone.  /proc/mdstat
> just gives me this:
> sudo mdadm /dev/md0 --add /dev/sde1
> mdadm: error opening /dev/md0: No such file or directory
> david at Archive:~$ cat /proc/mdstat
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
> [raid4] [raid10]
> md_d0 : inactive sdf1[3](S)
>       976759936 blocks
>
>        /dev/sdf1 was the last drive I added to /dev/md0.  /dev/sde1 was the
> one I couldn't add due to the "device busy" error.  Before the reboot,
> /dev/sdb, c, d, and f all showed in /proc/mdstat.  What the heck?  Why
> would a RAID array that was fully built and appeared to be fine before
> the reboot just vanish after?  And why does sdf1, and only sdf1, still
> show up in /proc/mdstat?

Check the boot log.  It may failed during boot and is not active.

t this point I would suspect hardware faults, BIOS faults, kernel bug,
or a faulty drive (not necessarily in that order).  Try building a
smaller array with just sde and another drive using the same ports.
Check their SMART status using smartctl just in case.

>        While we're on the subject, I've got one other question:  when adding a
> drive to a RAID array with mdadm, how do you tell mdadm to treat the
> drive as a member of the main array, or as a hot spare?  So far, all the
> HOWTOs I've found on adding drives just use --add for both actions,
> without any apparent differentiation between regular and spare drives.

I haven't done that yet.  It might be assumed by mdadm if the array
already has enough members.