Re: RAID5 losing initial synchronization on restart when one disk is spare

[Hubert Verstraete <hubskml@free.fr>]

Hubert Verstraete wrote:
> Hello
>
> According to mdadm's man page:
> "When creating a RAID5 array, mdadm will automatically create a degraded
> array with an extra spare drive. This is because building the spare
> into a degraded array is in general faster than resyncing the parity on
> a non-degraded, but not clean, array. This feature can be over-ridden
> with the --force option."
> 
> Unfortunately, I'm seeing a kind of bug when I create a RAID5 array with 
> an internal bitmap, then stop the array before the initial 
> synchronization is done and restart the array.
> 
> 1° When I create the array with an internal bitmap:
> mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -b internal -R /dev/sd?
> I see the last disk as a spare disk. After the restart of the array, all 
> disks are seen active and the array is not continuing the aborted 
> synchronization!
> Note that I did not use the --assume-clean option.
> 
> 2° When I create the array without a bitmap:
> mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -R /dev/sd?
> I see the last disk as a spare disk. After the restart of the array, the 
> spare disk is still a spare disk and the array continues the 
> synchronization where it had stopped.
> 
> In the case 1°, is this a bug or did I miss something?
> Secondly, what could be the consequences of this non-performed 
> synchronization ?
> 
> Kernel version: 2.6.26-rc4
> mdadm version: 2.6.2
> 
> Thanks,
> Hubert

For the record, the new stable kernel 2.6.25.6 has the same issue.
I thought maybe the patch "md: fix prexor vs sync_request race" could 
have fixed this, unfortunately not.

Regards,
Hubert
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