[linux-lvm] recover volume group & locical volumes from PV?

[Rainer Fügenstein]

hi,

I discovered that the lvm text files recovered from lost+found where out 
of date. I got as far as reconstructing such a lvm config file from data 
stored in the first MB, but after some syntax errors and values that 
didn't look consistent, I decided to do a re-install.

fortunately, didn't lose much data.

thank you both for your help, provided valuable insight.

cu


On 13/05/2019 10:37, Zdenek Kabelac wrote:
> Dne 12. 05. 19 v 0:52 "Rainer Fügenstein" napsal(a):
>> hi,
>>
>> I am (was) using Fedora 28 installed in several LVs on /dev/sda5 (= PV),
>> where sda is a "big" SSD.
>>
>> by accident, I attached (via SATA hot swap bay) an old harddisk
>> (/dev/sdc1), which was used about 2 months temporarily to move the volume
>> group / logical volumes from the "old" SSD to the "new" SSD (pvadd,
>> pvmove, ...)
>>
> 
> Hi
> 
> I don't understand how this could have happened by accident.
> lvm2 provides strong detection of duplicated devices.
> It also detects older metadata.
> 
> So you would have to put in 'exact' but just old 'copy' of your device
> and at the same time drop out the original one -  is that what you've 
> made ??
> 
>> this combination of old PV and new PV messed up the filesystems. when I
>> noticed the mistake, I did a shutdown and physically removed /dev/sdc.
>> this also removed VG and LVs on /dev/sda5, causing the system crash on
>> boot.
>>
>>
>> [root at localhost-live ~]# pvs
>>    PV         VG              Fmt  Attr PSize    PFree
>>    /dev/sda5                  lvm2 ---   <47.30g <47.30g
>>    /dev/sdc1  fedora_sh64     lvm2 a--  <298.09g 273.30g
>>
>> is there any chance to get VG and LVs back?
> 
> 
> VG & LV are just 'terms' - there is no 'physical-content' behind them - 
> so if you've already used your filesystem and modified it's bits on a 
> device - the physical content of your storage is simply overwritten and 
> there is no way to recover it's content by just fixing lvm2 metadata.
> 
> lvm2 provides command:  'vgcfgrestore' - which can restore your older 
> metadata content (description which devices are used and where the 
> individual LVs use their extents - basically mapping of blocks) - 
> typically in your /etc/lvm/archive directory - and in the worst case - 
> you can obtain older metadata by scanning 1st. MiB of your physical 
> drive - data are there in ascii format in ring buffer so for your small 
> set of LVs you likely should have there full history.
> 
> When you put back your original 'drive set' - and you restore your lvm2 
> metadata to the point before you started to play with bad drive - then 
> your only hope is properly working 'fsck' - but there is nothing how 
> lvm2 can help with this.
> 
> Regards
> 
> Zdenek
> 
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