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Date: Tue, 29 Jun 2004 11:47:46 -0400
From: "Kevin A. Pieckiel" <pieckiel+freebsd-questions@sdf.lonestar.org>
To: "Cordula's Web" <cpghost@cordula.ws>
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cc: freebsd-questions@freebsd.org
Subject: Re: Snapshot question
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On Tue, Jun 29, 2004 at 04:56:54PM +0200, Cordula's Web wrote:
> Are you sure you are comparing against the correct snapshot? If you use
> dump -L, the snapshot is created, opened, and immediately unlinked,
> then the open file is saved. After dump exits, the snapshot file is
> pysically released.
> 
> Are you creating a snapshot manually? What commands do you use exactly?

I'm actually using tar because my data store is larger than my tapes,
and I can't find a way to get dump to change tapes for me automatically
(something akin to tar's --new-volume-script parameter).

The relevant commands I use are as follows (this just shows the /var
parittion, but I make snapshots and mount all important partitions
in /mnt/backup before I run tar):

cd /
mksnap_ffs /var /var/.snap/backup.snap
mdconfig -a -t vnode -f /var/.snap/backup.snap -u 6
mount -r /dev/md6 /mnt/backup/root.var
tar -cvf ${BACKUP_DEVICE} --totals --preserve \
    --blocking-factor ${BACKUP_BLOCKSIZE} --block-number --multi-volume \
    --new-volume-script ${PROGROOT}/next.sh \
    --newer-mtime "${TIMESTAMP}" ${BACKUP_FLAGS} \
    ${BACKUP_PATHS} >> ${LOGFILE} 2>&1
tar --compare -f ${BACKUP_DEVICE} --blocking-factor ${BACKUP_BLOCKSIZE} \
    --multi-volume --new-volume-script ${PROGROOT}/next.sh >> ${COMPAREFILE} 2>&1
umount /mnt/backup/root.var
mdconfig -d -u 6
rm -f /var/.snap/backup.snap

Here, BACKUP_PATHS is set as follows:

BACKUP_PATHS="/mnt/backup"