On 11/12/2014 01:11 PM, Josh Fisher wrote:
> On 11/8/2014 1:35 PM, Dmitri Maziuk wrote:
> I think there is some confusion about this due to "multiple devices"
> being an ambiguous term. There is a difference between "multiple devices
> that are only attached one at a time" and "multiple devices that may be
> attached all at the same time". For disk storage, including virtual disk
> autochanger, the "device" is a directory, and in almost all cases it is
> in fact the mount point of a filesystem partition. The virtual
> autochanger described in 2.2 will work with any filesystem mounted at
> /disk, so multiple disk drive partitions CAN be used, but ONLY one at a
> time. This then works similarly to tape.
If this were true you couldn't use more than one tape drive of the same
kind, e.g. the jukeboxes with 2 and more drives would only use one.
Perhaps that is the case and nobody knows about it because people who
can shell out $15K+ on a tape library don't use bacula.
... When the disk drive partition
> gets full, you must unmount the current disk partition and mount the
> next one
... The not so obvious caveat is that in order to use
> hot-swappable drives with a disk Device you MUST use Requires Mount,
> particularly if you are using automatic volume labeling.
Hmm. So I could in theory come up with Mount Command that mounts each
disk in a list (and optionally checks for free space and mounts the next
one if there isn't any) and it all will "Just Work(tm)". Maybe someday
I'll have copious free time and a fresh supply of round tuits...
...
> The other issue, using multiple simultaneously mounted filesystems, is
> not so clear. Each Device resource associated with an autochanger can
> specify a different Archive Device path. To do so, it is also necessary
> to use a different Media Type for each filesystem. Bacula expects to be
> able to load any volume of a particular Media Type into any Device
> having that same Media Type. A volume file located in one Device's
> Archive Device directory cannot be "loaded" into another Device with a
> different Archive Device directory
Again, if as Kern says it's all implemented the same way, then you also
should not be able to load an LTO-6 tape in "just any" LTO-6 drive.
You'd have to give them media types (e.g.) lto-6-mt0 and lto-6-mt1 and
the tapes would only be loadable into /dev/mt0 and /dev/mt1 resp.
If that isn't the case then there are significant differences in how
tape and disk backups are coded in bacula. Then the "works similarly to
tape" assumption is incorrect.
[vchanger]
... It is open source (GPL v2) and
> available on SourceForge, so no "buying it off" is needed.
Figure of speech. Though I've no idea what legaleze comes with bacula
enterprise and how it might play with your gpl'ed code. (Bareos folks
might know more about that.)
> It just so happens that I have recently had some time to update
> vchanger.
Cool. Please post a message to the list when it's out.
Thanks
--
Dimitri Maziuk
Programmer/sysadmin
BioMagResBank, UW-Madison -- http://www.bmrb.wisc.edu
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