Leslie Rhorer wrote:
>> It performs the same function as the disk-changer shell script that
>> ships with Bacula, but with some enhancements. Removable drives are
>> treated as magazines containing some number of volume files. An
>> autochanger has some number of magazine bays into which magazine drives
>> can be "inserted".
>>
>
> I don't think an auto-changer script would be useful for me. I'm
> only going to have one external hot-swap slot. Back to one of my original
> questions, though: how does Bacula identify a particular backup drive to the
> user? Suppose, for example, a requested restore requires drive #7 of a 10
> drive backup set. How does Bacula identify the drive to the user? How does
> it know and what does it do if the user inserts the wrong drive?
> (Obviously, part of the answer to the latter is the necessary information
> won't be on the drive, but surely it doesn't have to scan the entire drive
> to find that out?)
>
It doesn't identify drives. It identifies volumes that are needed.
Backups are made to volumes, which on disk are regular files on a
filesystem partition, not the raw drive. So, for example, if you had 3
volumes on each drive then you might name them drive01vol1, drive01vol2,
and drive01vol3 for drive 1, drive02vol1, drive02vol2, and drive02vol3
for drive 2, and etc. When Bacula asked to mount a volume labeled
'drive07vol2' you would then know that it was on drive 7. If you put the
wrong drive in, then it would not contain volume 'drive07vol2' and
Bacula would complain.
>
>> Each magazine has the same number of slots. The total
>> number of autochanger slots is the number of bays times the number of
>> slots per magazine. There can be any number of virtual drives (<= the
>> number of virtual slots). The virtual drive (ie. ArchiveDevice) can be
>> loaded from any of the magazines currently inserted into one of the
>> bays. Removable drives acting as magazines can be assigned to the
>> autochanger by filesystem UUID. This allows for a simple autofs map that
>> makes swapping drives pretty much plug-n-play, at least on systems with
>> udev (or Windows). You still have to issue an update slots in bconsole
>> to tell Bacula which volumes are in which slots, but it makes the
>> operation at least as simple as changing a tape magazine.
>>
>
> You lost me a little, here. This portion makes it sound as if the
> autochanger might be useful for a hot-swappable drive, but I'm not quite
> seeing the whole picture - or its advantages.
>
>
Indeed, it is primarily for hot-swappable drives such as USB, 4-drive
hot-swap SATA enclosures, etc. It also allows multiple virtual drives,
which is useful when multiple pools are used to run multiple concurrent
jobs. Rather than having to specify which jobs use which devices, all
jobs use the same autochanger device.
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