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



On Thu, 1 May 2008, Gerry Reno wrote:

Mikulas Patocka wrote:
... 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.
Why? What value is the old snapshot at this point? You just had a system reboot in the middle of a snapshotted backup so all you need to do is get the system up, redo another snapshot and retake your backup. I'm not interested in the old snapshot.

If you use snapshots for something other than backups (for example version-control using snapshots --- to enable admin to revert changes if he messes something), then the snapshot is valuable and should survive reboot.

Anyway, placing a ramdisk to volume group is bad idea and it must not be done on any production system --- note that any lvcreate, lvconvert, etc command can allocate anything on that ramdisk --- without the administrator knowing it. --- so I don't see any reason why we should do extra hacks to lvm for people who placed ramdisk into vg.


To use temporary storage for snapshot, a special command for lvm would be more appropriate --- a command that would setup snapshot and write nothing about it to metadata, so that the snapshot would be forgotten on next reboot --- then, you can setup the snapshot on any device outside the volume group. You can already do this with dmsetup.

Mikulas


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