Hi,
bacula is able to back up data from block devices by listing them as dedicated
files in filesets. During restore, data is expected to be dumped back to these
devices.
However, this results in ambiguities when restoring to a location ("where"
statement) other than the system root. E.g., restoring to a temporary
directory/location (I'm using /tmp in this example) results in the device file
being created in the respective location, and the data being fed to that
device -- possibly resulting the data being written to the "original" space.
E.g., if a device /dev/sda1 was backed up, a device file /tmp/dev/sda1 will be
created with the major/minor pair of /dev/sda1 -- and data being written to
that device file will overwrite the system's /dev/sda1 -- not in an
alternative location, as the user might expect.
Interestingly, if a (file!) /tmp/dev/sda1 pre-exists, data is written into
that file; the block device is not recreated. That file can e.g. be an empty
file (touch /tmp/dev/sda1), or a loopback device (dd if=/dev/zero of=foo...;
mknod /tmp/dev/sda1 b 7 1; losetup /tmp/dev/sda1 foo).
I am unhappy with that situation; restoring with a given "where" location
should never ever write data into the system's devices. At the same time, I
was only able to restore data that was originally stored in a device to a file
by the "hack" described above.
As a side note, interestingly, the linux kernel happily accepted data for a
block device that it did not have an appropriate module for during a restore.
I was handling DRBD devices; after a backup of a DRBD device on one machine, I
did not encounter any error messages on a machine that did not have an
appropriate DRBD setup during restore. Data was never restored, however.
What do you think? Is the behavior as it is the way you'd expect it to be?
Would you rather think that the current behavior should be changed and
documented in a better way?
>From my point of view, it would be sensible to
a) _always_ create files (instead of block devices) for restored data when an
alternative location is given during restore
and/or
b) having a separate restore flag ("dump to file" vs. "dump to device") for
block device restore behavior
Thx
Bastian
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