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

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This article answers a FAQ (frequently asked question).

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.,


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 tapedev or tpchanger. So, for example

 tpchanger "chg-disk:/path/to/vtapes"


 tapedev "chg-robot:/dev/sg2"


 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.

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