[rear-users] Restoring mdadm system to a single-disk destination fails

Johannes Meixner jsmeix at suse.de
Tue Jul 24 11:23:19 CEST 2012


Hello,

On Jul 23 14:10 Cal Sawyer wrote (excerpt):
> Restored a CentOS5 (mdadm) system to a single-disk ESXi VM.
...
> In addition, /mnt/local/etc/fstab is an exact copy of the
> original, so booting the restored machine will fail

Perhaps your etc/fstab comes from the backup restore?

In the past I noticed "funny" mounted filesystems after
a "rear recover" and those came from the etc/mtab file
from the backup restore.
On newer systems /etc/mtab is only a link to /proc/self/mounts
which is o.k. in the backup but a regular file /etc/mtab in the
backup would overwrite the current one in the recreated system
with outdated content from the time when the backup was made.

There is the general problem that some files in the backup
may no longer match in the recreated system.
In general all files which are made anew when "rear recover"
does the basic system setup must not be overwritten afterwards
when the backup is restored.
There is the EXCLUDE_RESTORE option but I don't know to what extent
Rear 1.13.0 excludes by default such files from the backup restore.

There is the option EXCLUDE_BACKUP (formerly BACKUP_PROG_EXCLUDE)
to exclude certain files when the backup is made.
But EXCLUDE_BACKUP and EXCLUDE_RESTORE are not necessarily the same.
It depends on how different the recrearted system is which exact
files must be excluded from the backup restore and that files may
not be known in advance by the admin when the backup is made.

I think in general the backup should be complete and not depend
on recreation of particular files by "rear recover" - i.e. the
backup should be a generic complete backup and not a special
kind of "crippled backup only for Rear".
For example /etc/fstab from backup.tar.gz may contain additional
entries (e.g. manually added entries) which may not be automatically
recreated by "rear recover". Therefore I think it is recommended
to have /etc/fstab in the backup and exclude it only if needed
when the backup is restored.


I think a good default for such a functionality could become
in particular tricky for the various external backup methods.


Kind Regards
Johannes Meixner
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