Re: [linux-lvm] Major problems after soft raid 5 failure

[malahal@us.ibm.com]

Colin Faber [cfaber@gmail.com] wrote:
> Hi,
>
> malahal@us.ibm.com wrote:
>> Colin Faber [cfaber@gmail.com] wrote:
>>   
>>> was unavailable. After searching around I kept coming back to suggestions 
>>> stating that removal of the missing device from the volume group was the 
>>> solution to getting thing back online again. So using 'vgreduce 
>>> --removemissing raid' then 'lvchange -ay raid' to update the changes - 
>>> Neither command errored and vgreduce noted that 'raid' was not available 
>>> again.
>>>     
>>
>> Since your LV (array) is most likely allocated on md1 that disappeared,
>> you really want --partial (lvm command) rather than --removemissing.
>> Your metadata is updated and any knowledge about 'array' LV is now
>> almost gone due to the above 'vgreduce'. I say almost gone because it
>> might be there but you really need true LVM expertise now!
>>
>> Did you save a copy of your old LVM metadata before the reboot? See your
>> /etc/lvm/backup/raid has any reference to 'array' LV at all.
>>   
> Yes, it's still there (well /etc/lvm/archive/). So how do I back out of 
> this after I've already run removemissing? If I try and restore the old vg 
> backup it just tells me that it can't restore it because the uuid is 
> missing for md1.
>
> By the way, thank you very much for the response. Any suggestions and help 
> are greatly welcome.

Isn't there a force option to vgcfgrestore?  There maybe an easier way,
but I have not done much of LVM administration. Looking at the end of
'vgcfgrestore', you can create a PV that will have the same uuid and
size as your failed md1 using 'pvcreate ...'.

I would say, create a sparse file and use losetup to create a block
device against it. Then use 'pvcreate' to create an identical device
with md1's uuid. After that, use vgcfgrestore.

Thanks, Malahal.
PS: Try posting to dm-devel (they may suggest an easier method)