View source for FAQ:What's the difference between a device and a changer? Between tapedev and tpchanger?

{{FAQ Header}}

= Devices and Changers =
The best way to distinguish a device from a changer is by analogy to real, physical tapes.  If you want to use more than one tape in your Amanda configuration, you need:
 * some tapes
 * a drive
 * something to swap tapes (either a robot or a junior sysadmin)

Amanda's terms for these are, respectively:
 * volumes
 * devices
 * changers

When Amanda needs a tape, it asks the changer for a device, and the changer does whatever's necessary - moving a tape into a drive or adjusting some symlinks for vtapes - and returns an appropriate device.

The model gets a little less obvious for things like VFS devices and Amazon S3, but it's still there!  For S3 backups, for example, each volume has its own device, e.g.,
;Volume: DailySet-004
;Device: <tt>s3:mybucket/TAPE-004</tt>
;Changer: <tt>chg-multi:s3:mybucket/TAPE-{001,002,003,004,005,006,007}</tt>

= Configuration (tapedev and tpchanger) =
New configurations only need to specify a changer.  That changer will produce devices.  In order to ensure backward compatibility, that changer can be specified in ''either'' <tt>tapedev</tt> or <tt>tpchanger</tt>.  So, for example
  tpchanger "chg-disk:/path/to/vtapes"
or
  tapedev "chg-robot:/dev/sg2"
or
  tpchanger "my-changer-config"
  define changer "my-changer-config" {
    ...
  }

If you are looking at an older configuration, you may find both set along with some other options, e.g.,
  tpchanger "chg-zd-mtx"
  tapedev "/dev/nst0"
  changerdev "/dev/sg0"
  changerfile "/etc/amanda/myconfig/changer.conf"

If you have such a configuration, it ''should'' still work.  If you want to upgrade it to use functionality available in newer versions of Amanda, consult the mailing list or #amanda.
{{Languages}}