Re: Missing md superblock on added devices after grow ...

[rdc <denrdc@gmail.com>]

On Saturday 23 May 2009 23:05:35 NeilBrown wrote:
> On Sun, May 24, 2009 1:03 am, rdc wrote:
> > Yesterday i grew my 4*500GB raid5 array to 7*500GB. The reshape operation
> > ended succesfully according to the logs :
> >
> > May 22 22:24:56 [kernel] md: md2: reshape done.
> > May 22 22:24:56 [kernel] RAID5 conf printout:
> > May 22 22:24:56 [kernel]  --- rd:7 wd:7
> > May 22 22:24:56 [kernel]  disk 0, o:1, dev:dm-3
> > May 22 22:24:56 [kernel]  disk 1, o:1, dev:dm-0
> > May 22 22:24:56 [kernel]  disk 2, o:1, dev:dm-2
> > May 22 22:24:56 [kernel]  disk 3, o:1, dev:dm-1
> > May 22 22:24:56 [kernel]  disk 4, o:1, dev:dm-8
> > May 22 22:24:56 [kernel]  disk 5, o:1, dev:dm-6
> > May 22 22:24:56 [kernel]  disk 6, o:1, dev:dm-5
>
> The devices in your array are dm-xx devices, but....
>
> > However, upon restarting this morning the grown array was no longer
> > detected,
> > and my investigation revealed that the 3 device that were added do not
> > contain
> > an md superblock at all !
> >
> > One of the 3 new devices :
> > mdadm --examine -v /dev/sdb1
> > mdadm: No md superblock detected on /dev/sdb1.
>
> ... you are looking on sdxx devices for the superblock.  This
> seem to me to be a strange thing to do.
> What does
>    mdadm --example /dev/mapper/whatever
> show?

mdadm --examine -v /dev/mapper/sdb1
mdadm: No md superblock detected on /dev/mapper/sdb1

>
> What exactly are the dm-xx devices?

Well the dm-xx devices are just the same partitions mapped into dm by the 
mapper. It just creates /dev/mapper/sdXX  devices which are the same as the 
underlying /dev/sdxx devices. I removed the mappings for clarity. The names 
always show up as dm-XX from a kernel perspective.

>
> NeilBrown