First of all thanks to Kern and Bacula Systems for making the "Best 
Practices for Disk Based Backup" and "Disk Back Design" documents 
available.

I have been playing around with the best way for doing concurrent 
backups for a while and these documents have helped my understanding 
considerably.  Using a Virtual Autochanger in particular seems an 
elegant way of doing what I would like to do.

However, I am seeing some behaviour in my testing that I did not expect 
and I need some input.

At a high level what I am trying to do is use a Virtual Autochanger to 
write to multiple volumes in the same pool concurrently.

At the moment I have two devices limited to one concurrent job each.  
Which, if I have understood things correctly, means that I should have 
two jobs running concurrently writing to separate volumes.  The schedule 
below kicks off eight jobs simultaneously with the number of devices 
limiting concurrency.

This issue that I am having is that the first job gets FileChgr1-Dev1 
and a volume as expected.

The second job gets device FileChgr1-Dev2 as expected, but always says 
"Cannot find any appendable volumes." and issues a mount request.  There 
are multiple purged volumes with the recycle flag set available in the 
IncPoool pool. Even if there weren't, the pool has Auto Labelling 
configured and has not reached the MaximumVolumes limit, so there should 
"always" be a volume available.

Other jobs continue to use the FileChgr1-Dev1 as it becomes available 
while FileChgr1-Dev2 is waiting for a volume.

The second job eventually retries on FileChgr1-Dev2, gets an available 
volume and successfully completes without any operator intervention.

After this the remaining jobs utilise both FileChgr1-Dev1 and 
FileChgr1-Dev2 as they become available as I expected.

Is this behaviour expected (I am assuming some sort of race condition at 
the start of the schedule with multiple jobs trying to get a volume at 
the same time) or am I trying to do something fundamentally wrong here?

My configuration is:

Pool {
   Name = IncPool
   Pool Type = Backup
   Volume Use Duration = 23 hours
   Recycle = yes
   Action On Purge = Truncate
   Auto Prune = yes
   Maximum Volumes = 50
   Volume Retention = 2 weeks
   Storage = FileStorage01
   Next Pool = "IncPoolCopy"
   Label Format = "IncPool-"
}

Storage {
   Name = FileStorage01
   Address = 192.168.42.45
   SDPort = 9103
   Password = ***************************
   Device = FileChgr1
   Media Type = File01
   Maximum Concurrent Jobs = 10
   Autochanger = yes
}

Autochanger {
   Name = FileChgr1
   Device = FileChgr1-Dev1, FileChgr1-Dev2
   Changer Command = /dev/null # For  7.0.0 and newer releases.
   # Changer Command = "" # For 5.2 and older releases.
   Changer Device = /dev/null
}

Device {
   Name = FileChgr1-Dev1
   Drive Index = 0
   Media Type = File01
   Archive Device = /bacula_storage/FileDevice
   LabelMedia = yes;
   Random Access = Yes;
   AutomaticMount = yes;
   RemovableMedia = no;
   AlwaysOpen = no;
   Maximum Concurrent Jobs = 1
   VolumePollInterval = 5s
   Autochanger = yes
}

Device {
   Name = FileChgr1-Dev2
   Drive Index = 1
   MediaType = File01
   ArchiveDevice = /bacula_storage/FileDevice
   LabelMedia = yes;
   RandomAccess = Yes;
   AutomaticMount = yes;
   RemovableMedia = no;
   AlwaysOpen = no;
   MaximumConcurrent Jobs = 1
   VolumePollInterval = 5s
   Autochanger = yes
}

Schedule {
   Name = "DefaultBackupCycle"
   Run = Level=Full 1st sun at 00:10
   Run = Level=Differential 2nd-5th sun at 00:10
   Run = Level=Incremental mon-sat at 00:10
}

Thanks

Mike

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