Re: Degraded raid5 returns mdadm: /dev/hdc5 has no superblock - assembly aborted

[Daniel Pittman <daniel@rimspace.net>]

On 8 Jul 2005, Molle Bestefich wrote:
>> On 8 Jul 2005, Melinda Taylor wrote:
>>> We have a computer based at the South Pole which has a degraded raid 5
>>> array across 4 disks. One of the 4 HDD's mechanically failed but we have
>>> bought the majority of the system back online except for the raid5
>>> array. I am pretty sure that data on the remaining 3 partitions that
>>> made up the raid5 array is intact - just confused. The reason I know
>>> this is that just before we took the system down, the raid5 array
>>> (mounted as /home) was still readable and writable even though
>>> /proc/mdstat said:
>
> On 7/8/05, Daniel Pittman wrote:
>> What you want to do is start the array as degraded, using *only* the
>> devices that were part of the disk set.  Substitute 'missing' for the
>> last device if needed but, IIRC, you should be able to say just:
>>
>> ] mdadm --assemble --force /dev/md2 /dev/hd[abd]5
>>
>> Don't forget to fsck the filesystem thoroughly at this point. :)
>
> At this point, before adding the new disk, I'd suggest making *very*
> sure that the event counters match on the three existing disks. 
> Because if they don't, MD will add the new disk with an event counter
> matching the freshest disk in the array.  That will cause it to start
> synchronizing onto one of the good disks instead of onto the newly
> added disk....  Happened to me once, gah.

Ack!  I didn't know that.  If the event counters don't match up, what
can you do to correct the problem?  

    Daniel
-- 
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