qvm-backup can create broken backup archive

[marmarek]

Reported by marmarek on 18 Sep 2014 23:47 UTC
Because of tar bug, some VMs cannot be backed up correctly. This affects:

• every VM, whose root.img/private.img is at least 50GB and have really scattered data (so there is a lot "holes" in the image). Concretely, description of such holes is larger than 100MB (info about one hole use 24 bytes),
• some standalone/template VMs, whose private.img/root.img (used) size is about multiple of 100MB, and description of the holes in the other image is at least 3MB; this doesn't affect every such VM, only those, where root.img/private.img is such placed in dom0 filesystem, that the first one is the one of N*100MB size.

It looks like it isn't fixable without changing tar archive format, so the solution would be to change our backup format (to not use multi-volume tar feature).

Migrated-From: https://wiki.qubes-os.org/ticket/902

[marmarek]

Comment by marmarek on 18 Sep 2014 23:52 UTC
Because of proximity to R2 final release, we've decided to not change backup format just before the release. Instead we've implemented #863. And made restore process more defensive, namely do not fail when archive of one VM is broken.

If someone encounter this problem (hopefully during backup verification, not a real need to restore the backup...), one can backup such a VM manually, simply copying its root.img/private.img. Then during restore, replace restored (broken) files with those copied manually.

[marmarek]

Comment by marmarek on 18 Sep 2014 23:52 UTC
Because of proximity to R2 final release, we've decided to not change backup format just before the release. Instead we've implemented #863. And made restore process more defensive, namely do not fail when archive of one VM is broken.

If someone encounter this problem (hopefully during backup verification, not a real need to restore the backup...), one can backup such a VM manually, simply copying its root.img/private.img. Then during restore, replace restored (broken) files with those copied manually.

[marmarek]

Modified by marmarek on 28 Sep 2014 02:15 UTC

[marmarek]

Modified by marmarek on 28 Sep 2014 02:15 UTC

[marmarek]

Comment by marmarek on 8 Oct 2014 14:09 UTC
http://git.qubes-os.org/?p=marmarek/core-admin.git;a=commit;h=fc0c0adff8e8c96fb74c51d7973216c8ffd76c58

[marmarek]

Comment by marmarek on 8 Oct 2014 14:09 UTC
http://git.qubes-os.org/?p=marmarek/core-admin.git;a=commit;h=fc0c0adff8e8c96fb74c51d7973216c8ffd76c58