Re: [Bacula-users] backup to multiple disks
2013-05-05 09:31:02
On 5/3/2013 4:56 PM, Dimitri Maziuk wrote:
> On 05/03/2013 02:53 PM, Josh Fisher wrote:
>
>> ... What you are
>> considering would require a new device assignment each time a new volume
>> is needed. While possible, it is way more complex that it appears at
>> first glance.
> PS. I think the potentially worse can of worms is when you have multiple
> devices and some of them are autochangers and some aren't, and while
> switching to the next "already mounted" device should be cheaper than
> auto-changing the tape in the current device, if the current autochanger
> is actually a vchanger over mounted partitions it isn't, and so on and
> so forth.
The drives inside of an autochanger are treated like any other device,
for the most part. An autochanger resource only groups them together so
that assigning an autochanger resource to a storage resource allows the
device selection to be limited to ONE of the devices belonging to that
autochanger. The autochager isn't assigned to a job at startup, but
rather one particular drive (device resource) belonging to that
autochanger. That assignment doesn't change for the life of the job.
Reassigning a job's device at every media change is possible, it is just
more complicated and increases the likelihood of introducing a race
condition when more than one job is requesting new media at the same
time. There are two different operations happening, device assignment
and media assignment. It would be necessary to make selecting both at
the same time an atomic operation. So it is just the "normal" complexity
of multi-threaded programming, which is always much more complex than it
seems. So I think the Bacula devs have just chosen the safety and
robustness of keeping it simple, rather than the risk of added
flexibility. It's just an engineering choice.
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- Re: [Bacula-users] backup to multiple disks, (continued)
- [Bacula-users] vchanger: 0 slots problem, Dimitri Maziuk
- Re: [Bacula-users] vchanger: 0 slots problem, Josh Fisher
- Re: [Bacula-users] vchanger: 0 slots problem, Dimitri Maziuk
- Re: [Bacula-users] vchanger: 0 slots problem, Josh Fisher
- Re: [Bacula-users] vchanger: 0 slots problem, Dimitri Maziuk
- Re: [Bacula-users] backup to multiple disks, Radosław Korzeniewski
- Message not available
- Re: [Bacula-users] backup to multiple disks, Dimitri Maziuk
- Re: [Bacula-users] backup to multiple disks,
Josh Fisher <=
- Re: [Bacula-users] backup to multiple disks, Kern Sibbald
- Re: [Bacula-users] backup to multiple disks: SUMMARY, Dimitri Maziuk
- Re: [Bacula-users] backup to multiple disks, Radosław Korzeniewski
- Re: [Bacula-users] backup to multiple disks, Dimitri Maziuk
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