[mythtv-users] 1TB Volume running on top of RAID5 Vanished

[Len Reed]

Mache Creeger wrote:
> A 1TB volume storing 600GB of data has disappeared on my myth 
> server.  It was formatted with the XFS file system and was running on 
> top of a six disk (each disk being 200GB) 1TB RAID5 array.  On boot, 
> the volume does not exist and the RAID5 array is running with 5 out 6 
> drives.  The 6th drive is visible but not formatted.  In the past, 
> when you have 5 out 6 drives working, data integrity was 
> maintained.  In this case, however, the volume just disappeared.  Any 
> ideas on how to  recover my volume and its 600GB of data?

I'm assuming you're running software raid.  If you're running hardware 
RAID then little or nothing I write here will be relevant.

This happened to me, but I had an extra layer.  I had RAID5 (4 disks) 
plus LVM plus multiple logical volumes formatted with XFS.  One of the 
disks died: when I brought the system up the volume group was inactive 
because of the underlying RAID5 issue.  I manually activated the volume 
group (and maybe the logical volumes, too.  not sure).  It ran fine for 
a couple of days on 3 drives and then I replaced the bad drive and ran 
mdadm to add it to the array.

Does /proc/mdstat show 5 of 6 good drives?

I gather you don't have LVM and just formatted the entire 
/dev/md<whatever>.  I suspect your data are ok, but I'm not sure exactly 
what mdadm magic and/or xfs_check commands you'll need.  If your 6th 
drive is working but just isn't formatted, you could use mdadm to add 
the relevant partition back into the array and wait for it to rebuild 
that drive.  Then reboot the system and it will probably come up fine.