Re: Failed during rebuild (raid5)

[Andreas Boman <aboman@midgaard.us>]

On 05/05/2013 10:00 AM, Andreas Boman wrote:
> On 05/03/2013 08:26 AM, Ole Tange wrote:
>> On Fri, May 3, 2013 at 1:23 PM, Andreas Boman<aboman@midgaard.us>  
>> wrote:
>>
>>> This morning I came up to see the array degraded with two missing 
>>> drives,
>>> another failed during the rebuild.
>> I just started this page for dealing with situations like yours:
>> https://raid.wiki.kernel.org/index.php/Recovering_a_failed_software_RAID
>>
>>
>> /Ole
>
> After having ddrescue running all night, it dropped to copying at a 
> rate of 512B/s. I interrupted it and restarted, it stays at that 
> speed. shows no errors:
>
>    Press Ctrl-C to interrupt
>           Initial status (read from logfile)
>     rescued:   557052 MB,  errsize:       0 B,  errors:       0
>     Current status
>     rescued:     1493 GB,  errsize:       0 B,  current rate:      512 
> B/s
>        ipos:   937316 MB,   errors:       0,    average rate:   16431 
> kB/s
>           opos:   937316 MB,     time from last successful read:       
> 0 s
>           Copying non-tried blocks...
>
>
> However that is much too slow...
>
> Then, I decided to take a look at the superblocks and to my horror 
> discovered this:
>
> # mdadm --examine /dev/sd[b-g] >>raid.status
> mdadm: No md superblock detected on /dev/sdb.
> mdadm: No md superblock detected on /dev/sdc.
> mdadm: No md superblock detected on /dev/sdd.
> mdadm: No md superblock detected on /dev/sde.
> mdadm: No md superblock detected on /dev/sdf.
> mdadm: No md superblock detected on /dev/sdg.
>
> Can I recover still? What is going on here?
>
> Thanks,
> Andreas
>
Turns out the superblocks are there. I ran --examine on the disk instead 
of partition. OOps.

I still have the problem with ddrescue being very slow, it is running at 
512 B/s pretty much no matter what options I use. The ddrescued disk 
does NOT have a md superblock. I tried to ddrescue -i to skip and grab 
the last 3MB or so of the disk, that seemed to work, but I still don't 
have the superblock.

How do I find/recover the superblock from the original disk?

After that is done I'll try to get the array up with 4 disks, then add 
the spare and have it rebuild. After that I'll add a disk to go to raid 6.

Thanks,
Andreas