Re: How to fix this superblock?

[NeilBrown <neilb@suse.de>]

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On Mon, 16 Jun 2014 10:59:27 +0930 Pete <psid@riverland.net.au> wrote:

> Hi all. Please excuse, newbie here, finding out how much I don't know
> about md.
> 
> I have a RAID1 array which is running in degraded mode. When I try to
> re-add the device that used to be part of the array, I'm told that it's
> too small, though it used to be fine.
> 
> /proc/mdstat:
> 
> md1 : active raid1 sdc3[2]
>       2920305508 blocks super 1.0 [2/1] [_U]
> 
> When I try to re-add the device that used to be part of the array, mdadm
> says it's not large enough:
> 
> # mdadm --add /dev/md1 /dev/sdb3
> mdadm: /dev/sdb3 not large enough to join array
> 
> The partition tables hadn't changed when this started. Since then I've
> re-partitioned sdb to make sdb3 a few GB bigger, but it's still not
> large enough.
> 
> Looking at the working device's superblock, there's a heap of "failed"
> so I'm guessing that superblock has been damaged:
> 
> # mdadm -E /dev/sdc3
> 
> /dev/sdc3:
>           Magic : a92b4efc
>         Version : 1.0
>     Feature Map : 0x0
>      Array UUID : 129ec25f:f07e292a:5bf0829d:19793e6c
>            Name : pioneer:1  (local to host pioneer)
>   Creation Time : Thu Nov 21 21:19:12 2013
>      Raid Level : raid1
>    Raid Devices : 2
> 
>   Used Dev Size : 5841405976 (2785.40 GiB 2990.80 GB)
>      Array Size : 5840611016 (2785.02 GiB 2990.39 GB)
>       Used Size : 5840611016 (2785.02 GiB 2990.39 GB)
>    Super Offset : 5841406232 sectors
>           State : clean
>     Device UUID : 6bbc382c:244cf1ad:4fd61c87:4e40e592
> 
>     Update Time : Fri Jun 13 17:05:57 2014
>        Checksum : 93cf5353 - correct
>          Events : 444384
> 
>     Array Slot : 2 (failed, failed, 1, failed, failed, failed, failed,
> failed, failed, failed, failed, failed, failed, failed, failed, failed,
> failed, failed, failed, failed, failed, failed, failed, failed, failed,
> failed, failed, failed, failed, failed, failed, failed, failed, failed,
>  [snip]
> failed) Array State : _U 383 failed
> 
> 
> Could it be that whatever happened to the superblock on sdc3 is giving
> it an incorrect idea of the array size? Is that something I can fix?
> 
> Would I be better off creating a new array on sdb3+missing and copying
> data to that? Then I would zero the superblock on sdc3 and hopefully
> add it to the new array.
> 
> Would appreciate any help.

I suspect that upgrading to a newer mdadm would solve most of these problems.
What are you running? (mdadm -V)
Try:

  cd /tmp
  git clone git://neil.brown.name/mdadm
  cd mdadm
  make
  ./mdadm ......

NeilBrown

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