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Re: [Bacula-devel] request: Allow tape drives to be associated with autochanger resource on different host


Hello,

I can see that having separate machines driving different drives within a 
single autochanger could significantly improve speed, but Bacula already has 
significant difficulties dealing with multiple drives on a single machine, so 
this situation is far more complex in terms of communications an locking.  At 
the moment, I don't really see how to implement this, and in any case with 
the current equipment it is impossible because I don't have such an 
autochanger.

If you can find a programmer to design and implement this, I would be willing 
to discuss it with him/her to determine if it is feasible.  I hesitate to add 
this to the projects list until we find someone who can design and implement 
it.

Certainly in another couple of years this and the project about writing a 
single job to multiple drives at the same time will be very interesting 
projects, but I suspect that at the moment, unless someone can come up with 
some serious programming resources, these are a bit high end for Bacula (at 
the moment), especially since there are a number of really critical 
functionalities that are missing.

Best regards,

Kern

On Thursday 17 July 2008 18:05:54 Shad L. Lords wrote:
> Item  1: Allow tape drives to be associated with autochanger
>           resource on different host
>   Origin: Shad Lords <slords at lordsfam dot net>
>     Date: 17 July 2008
>   Status:
>
>     What: Allow tape drives that are part of an autochanger but are
>           connected to different hosts to be associated with the robot
>           autochanger.
>
>      Why: Many large autochangers that have multiple drives recommend
>           connecting drives up to different hosts to improve library
>           performance.  Doing so allows you to utilize full bus
>           bandwidth, split pool space, and utilize separate cpus to
>           achieve maximum throughput.
>
>     Note: A single robot controls multiple drives but is only connected
>           to one machine.  It is currently possible to work around
>           things by having remote hosts issue mtx commands over ssh but
>           nothing prevents multiple mtx commands from being issued at
>           the same time.
>
>    Note: By not being able to associate drives with their autochanger
>          you may not be taking full advantage of available drives for
>          backup/restore purposes.  In a job you can't specify multiple
>          libraries/drives, however all the drives on both (multiple)
>          hosts have access to all tapes in the library and there isn't
>          any reason any one of the drives couldn't be used for
>          backup/restore purposes.
>
>    Note: Sample config:
>
>          host1-sd.conf
>          =============
>
>          Autochanger {
>              Name = ait4-changer
>              Device = ait4-drive1
>              Device = ait4-drive2
>              Device = ait4-drive3
>              Device = ait4-drive4
>              Changer Command = "/usr/lib/bacula/mtx-changer ..."
>              Changer Device = /dev/sg0
>          }
>
>          Device {
>              Name = ait4-drive1
>              Archive Device = /dev/nst0
>              Drive Index = 0
>              Auto Changer = yes
>              Media Type = ait4
>              ...
>          }
>
>          Device {
>              Name = ait4-drive2
>              Archive Device = /dev/nst1
>              Drive Index = 1
>              Auto Changer = yes
>              Media Type = ait4
>              ...
>          }
>
>          host2-sd.conf
>          =============
>
>          Device {
>              Name = ait4-drive3
>              Archive Device = /dev/nst0
>              Drive Index = 2
>              Auto Changer = yes
>              Media Type = ait4
>              ...
>          }
>
>          Device {
>              Name = ait4-drive4
>              Archive Device = /dev/nst1
>              Drive Index = 3
>              Auto Changer = yes
>              Media Type = ait4
>              ...
>          }
>
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