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On 3/31/2014 12:04 PM, Randall Svancara
wrote:
Yes, it is a little confusing. A 2-drive autochanger is really 3 physical devices and usually has 3 SCSI LUNs, one for each actual tape drive and one for the robot that moves tapes in and out of the tape drives. Bacula handles this with the Autochanger resource defined in bacula-sd.conf which serves two purposes. One is to define the SCSI LUN and script used to send commands to the tape robot. The other is to determine which Device resources are the autochanger's actual tape drives, or in other words the list of Device resources that Bacula may assign to jobs that are reading/writing to the Autochanger resource. The actual tape drives in the autoloader are handled like any other tape drive with a Device resource definition in bacula-sd.conf. Thus the individual drives belonging to a multi-drive autoloader can be used as a stand-alone tape drive, if so desired, by specifying the SD's Device resource in the DIR's Storage resource. This is useful if there is a specific job that you want to dedicate a drive to. Perhaps there is a high priority job that is time constrained and must never have to wait on an available drive. In the normal use scenario, you specify the SD's Autochanger resource in the DIR's Storage resource, meaning that you want Bacula to select the first available drive and it doesn't matter which one gets selected.
I don't know what happens when two Device lines appear in the Storage resource. I suspect only one is used.
The only con with interleaving that I'm aware of is that it can make restores slow because it basically has to read all of the interleaved job data in order to restore one job.
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