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



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
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.

-- 
	      Stuart D. Gathman <stuart bmsi com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.


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