Can't recover half of a raid1

Can't recover half of a raid1

[Christopher Hicks]

We had a drive die in a RAID1 array.  I've tried to bring it back so we 
can migrate the data to a new machine and it keeps telling me "/dev/md0 
assembled from 1 drive - not enough to start the array."  I've tried 
everything I've found in the FAQ and wiki to no avail.  What am I missing?
Here's the log of what I've tried:

# mdadm -E /dev/hdb1
/dev/hdb1:
           Magic : a92b4efc
         Version : 00.90.00
            UUID : f8055b6f:766f7a3f:ad80d985:eb77d033
   Creation Time : Thu Feb 19 10:57:42 2004
      Raid Level : raid0
     Device Size : 102398208 (97.65 GiB 104.86 GB)
    Raid Devices : 2
   Total Devices : 2
Preferred Minor : 0

     Update Time : Sat Feb  3 22:56:54 2007
           State : clean
  Active Devices : 2
Working Devices : 2
  Failed Devices : 0
   Spare Devices : 0
        Checksum : 3cadf274 - correct
          Events : 0.44

      Chunk Size : 64K

       Number   Major   Minor   RaidDevice State
this     1       3       65        1      active sync   /dev/hdb1

    0     0       3        2        0      active sync   /dev/hda2
    1     1       3       65        1      active sync   /dev/hdb1
Personalities : [raid0] [raid1] [raid5] [raid6] 
# mdadm  -Af /dev/md0 /dev/hdb1
mdadm: /dev/md0 assembled from 1 drive - not enough to start the array.
# cat /proc/mdstat
md0 : inactive hdb1[1]
       102398208 blocks
unused devices: <none>


-- 
</chris>

If trees could scream, would we be so cavalier about cutting them down?
We might, if they screamed all the time, for no good reason.

Re: Can't recover half of a raid1

[CaT]

On Thu, Jul 10, 2008 at 10:00:05AM -0400, Christopher Hicks wrote:
> We had a drive die in a RAID1 array.  I've tried to bring it back so we 
...
>      Raid Level : raid0

These two things seem to contradict...

-- 
  "Police noticed some rustling sounds from Linn's bottom area
  and on closer inspection a roll of cash was found protruding
  from Linn's anus, the full amount of cash taken in the robbery."
    - http://www.smh.com.au/news/world/robber-hides-loot-up-his-booty/2008/05/09/1210131248617.html

Re: Can't recover half of a raid1

[Christopher Hicks]

On Fri, 11 Jul 2008, CaT wrote:
> On Thu, Jul 10, 2008 at 10:00:05AM -0400, Christopher Hicks wrote:
>> We had a drive die in a RAID1 array.  I've tried to bring it back so we
> ...
>>      Raid Level : raid0
>
> These two things seem to contradict...

Oh no.  I don't suppose there's any chance that mdadm is wrong about what 
RAID level that chunk was at.

-- 
</chris>

If trees could scream, would we be so cavalier about cutting them down?
We might, if they screamed all the time, for no good reason.

Re: Can't recover half of a raid1

[CaT]

On Thu, Jul 10, 2008 at 10:45:23AM -0400, Christopher Hicks wrote:
> On Fri, 11 Jul 2008, CaT wrote:
> >On Thu, Jul 10, 2008 at 10:00:05AM -0400, Christopher Hicks wrote:
> >>We had a drive die in a RAID1 array.  I've tried to bring it back so we
> >...
> >>     Raid Level : raid0
> >
> >These two things seem to contradict...
> 
> Oh no.  I don't suppose there's any chance that mdadm is wrong about what 
> RAID level that chunk was at.

I don't know to be honest. There are two possibilities as far as I can
see:

1. it is a raid 1 array so you might try creating it as raid 1 with a
drive missing and seeing if there's a valid filesystem there. don't know
if this will destroy useful data though.
2. you only think you had a raid1 array, in which case you're probably
screwed as the data would be interleved between the two drives.

-- 
  "Police noticed some rustling sounds from Linn's bottom area
  and on closer inspection a roll of cash was found protruding
  from Linn's anus, the full amount of cash taken in the robbery."
    - http://www.smh.com.au/news/world/robber-hides-loot-up-his-booty/2008/05/09/1210131248617.html