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

On Thu, 1 May 2008, malahal us ibm com wrote:

Gerry Reno [greno verizon net] wrote:
Milan Broz wrote:
... After reboot you have no ramdisk, and the Volume Group is incomplete
(because you didn't removed PV on ramdisk).

And this is no different than if snapshot was on any other device such as
esata-hdd, usb-hdd or usb stick.  LVM should handle this.  If the snapshot
device goes away, then just vgreduce it on the reboot.

If you mount the origin device with missing snapshot, you destroy the snapshot (even if you don't touch it). The snapshot can no longer be repaired.

So it is safer to not activate device in this case then destroy data.

Imagine, for example, you have origin and snapshot, you reconfigure disks in some weird way that the snapshot disk is inaccessible, you boot, and the system automatically starts without the snapshot. And you lose any data that you stored on that snapshot.

Trying to retrofit snapshot into existing systems is far easier if you can
use ramdisk, esata-hdd, usb-hdd, usb-stick because most systems have
allocated all space and rather than struggling through trying to compact
and reduce VG, LV, PV, partition, filesystem to gain space it is much
easier to use other devices.  And again this is something that LVM should
be able to handle.

You can with dmsetup (but it has deadlocks). Maybe someone could write non-deadlocky snapshot-managing tool that wouldn't depend on lvm vgs, pvs and lvs.


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