Re: [linux-lvm] F7 will not boot after running backup w/snapshot

[Gerry Reno <greno@verizon.net>]

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Stuart D. Gathman wrote:
> ZZZZOn Thu, 1 May 2008, Charles Marcus wrote:
>
>   
>> In Gerry's scenario here, if the snapshot volume had NOT been on a ram 
>> disk, would he have had the problem he had or not?
>>     
>
> Here is the snip from Fedora/RHEL for activating the VG containing
> the root filesystem (note: kernel modules and lvm command are contained in
> initrd filesystem, and do not depend on /lib/modules/...):
>
> ...
> echo "Loading dm-mod.ko module"
> insmod /lib/dm-mod.ko
> echo "Loading dm-mirror.ko module"
> insmod /lib/dm-mirror.ko
> echo "Loading dm-zero.ko module"
> insmod /lib/dm-zero.ko
> echo "Loading dm-snapshot.ko module"
> insmod /lib/dm-snapshot.ko
> echo Making device-mapper control node
> mkdmnod
> mkblkdevs
> echo Scanning logical volumes
> lvm vgscan --ignorelockingfailure
>   
So right ^^^here^^^ is where we need to test if old snapshot was 
read-only or read-write (how to do that? grep vgdisplay -v for some value?)
So maybe something like this?:

set removemissing flag false
if old snapshot is the only PV missing:
--if old snapshot was read-write:
------stop boot sequence
------show user some info about old snapshot
------prompt whether to remove the old snapshot from the VG so it can be 
activated
------if response yes:
----------set removemissing flag true
------else
----------alert user that manual action is required to correct problem 
related to old snapshot before VG can be activated
----------abort boot
--elsif old snapshot was read-only:
------set removemissing flag true
if removemissing flag true:
----vgreduce --removemissing VG PV(old snapshot)

Gerry

> echo Activating logical volumes
> lvm vgchange -ay --ignorelockingfailure  rootvg
> ...
>
> This will fail if any of the physical volumes are missing.  More logic
> in initrd is required to boot with missing PVs.
>
> So yes, a ram disk is guaranteed to be missing on reboot, and thus to 
> fail in the RH/Fedora distros.  There is no problem taking snapshots
> of the root fs otherwise.  If there is a robust way to reduce 
> missing PVs automagically in the above script from initrd, Fedora could
> use the contribution.
>
>   


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