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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