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Add instructions for ntfsclone (fixes #81)
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docs/faq.rst
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docs/faq.rst
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@ -48,6 +48,64 @@ and platform/software dependency. Combining Borg with the mechanisms provided
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by the platform (snapshots, hypervisor features) will be the best approach
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by the platform (snapshots, hypervisor features) will be the best approach
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to start tackling them.
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to start tackling them.
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How can I decrease the size of disk image backups?
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--------------------------------------------------
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Full disk images are as large as the full disk when uncompressed and might not get much
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smaller post-deduplication after heavy use. This is because virtually all file systems
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don't actually delete the data on disk (that is the place of so-called "secure delete")
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but instead delete the filesystem entries referring to the data. This leaves the random
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data on disk until the FS eventually claims it for another file. Therefore, if a hard
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drive nears capacity and files are deleted again, the change will barely decrease the
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space it takes up when compressed and deduplicated. Depending on the filesystem of the
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VM (or physical computer, if for some reason a normal filesystem backup can't be taken),
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there are several ways to decrease the size of a full image:
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Using ntfsclone (NTFS, i.e. Windows VMs)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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ntfsclone can only operate on filesystems with the journal cleared (i.e. turned-off
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machines) which somewhat limits its utility in the case of VM snapshots. However,
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when it can be used, its special image format is even more efficient than just zeroing
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and deduplicating. For backup, save the disk header and the contents of each partition::
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HEADER_SIZE=$(sfdisk -lo Start $DISK | grep -A1 -P 'Start$' | tail -n1 | xargs echo)
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PARTITIONS=$(sfdisk -lo Device,Type $DISK | sed -e '1,/Device\s*Type/d')
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dd if=$DISK count=$HEADER_SIZE | borg create repo::hostname-partinfo -
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echo "$PARTITIONS" | grep NTFS | cut -d' ' -f1 | while read x; do
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PARTNUM=$(echo $x | grep -Eo "[0-9]+$")
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ntfsclone -so - $x | borg create repo::hostname-part$PARTNUM -
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done
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# to backup non-NTFS partitions as well:
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echo "$PARTITIONS" | grep -v NTFS | cut -d' ' -f1 | while read x; do
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PARTNUM=$(echo $x | grep -Eo "[0-9]+$")
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borg create --read-special repo::hostname-part$PARTNUM $x
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done
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Restoration is similar to the above process, but done in reverse::
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borg extract --stdout repo::hostname-partinfo | dd of=$DISK && partprobe
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PARTITIONS=$(sfdisk -lo Device,Type $DISK | sed -e '1,/Device\s*Type/d')
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borg list --format {archive}{NL} repo | grep 'part[0-9]*$' | while read x; do
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PARTNUM=$(echo $x | grep -Eo "[0-9]+$")
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PARTITION=$(echo "$PARTITIONS" | grep -E "$DISKp?$PARTNUM" | head -n1)
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if echo "$PARTITION" | cut -d' ' -f2- | grep -q NTFS; then
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borg extract --stdout repo::$x | ntfsclone -rO $(echo "$PARTITION" | cut -d' ' -f1) -
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else
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borg extract --stdout repo::$x | dd of=$(echo "$PARTITION" | cut -d' ' -f1)
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fi
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done
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.. note::
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When backing up a disk image (as opposed to a real block device), mount it as
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a loopback image to use the above snippets::
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DISK=$(losetup -Pf --show /path/to/disk/image)
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# do backup as shown above
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sync $DISK
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losetup -d $DISK
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Can I backup from multiple servers into a single repository?
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Can I backup from multiple servers into a single repository?
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------------------------------------------------------------
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------------------------------------------------------------
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