Re: [opensuse] raid device mounting problem in Leap 42.2

[NeilBrown <neilb@suse.com>]

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On Fri, Jul 14 2017, Wols Lists wrote:

> On 13/07/17 23:46, Istvan Gabor wrote:
>> On Wed, 12 Jul 2017 17:05:17 +0300, Andrei Borzenkov wrote:
>>> On Wed, Jul 12, 2017 at 4:49 PM, Wols Lists <antlists@youngman.org.uk>
>>> wrote:
>>>>
>>>> But I suspect that going back into 12.2, and shrinking the filesystem
>>>> (MAKE SURE you shrink the md device, not the sd device)
>>>
>>> Quite the opposite. Attempting to shrink filesystem that is already
>>> effectively corrupted is potentially dangerous. So the right thing
>>> here is to stop md, backup superblocks (in case they will be
>> 
>> I am puzzled. Do I need to backup the raid superblock or the device
>> superblocks or all?

You cannot have too many backups.

>>                      How do I backup the superblock? I googled but only

mdadm --dump=/some/directory list of devices.

>> find how to recover from superblock backup.
>> 
> The best bet is to ask the linux-raid list what to do.
>
> For the raid list, this is the array I mentioned where the filesystem,
> and the partitions the raid was on, were the same size.

To the byte?  I really like to see the output of commands that report
sizes, rather than have someone claim "were the same size".  It isn't
that I don't trust you.  I just don't trust humans in general (myself included).

NeilBrown

>
> So we have a v1.0 mirror where the filesystem on the mirror uses up ALL
> the space on the md device, not just the free space that it's supposed
> to use, with all the issues that brings like filling up the filesystem
> will overwrite the superblock.
>
> So what's the best way to recover? Will just shrinking the filesystem
> bring everything back the way it should be, or are we better just
> mounting the original filesystem from one disk as if it weren't a
> mirror, and then recreating the mirror on the other disk, copying the
> data, and then adding the first disk back in to put everything back the
> way it should have been?
>
> Cheers,
> Wol
>
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