VFS Device

Introduction

Since release 2.4.3, Amanda supports the usage of a tape driver called "file". See the manual page of amanda, section OUTPUT DRIVERS, for more information.

As the name suggests, this driver uses files on disk as virtual tapes. Amanda can write to and read from virtual tapes, just like real tapes. A bunch of virtual tapes can even be manipulated with a changer.

Possible Uses

• Test installations: You can easily explore the rich features of Amanda on systems without tape drives. Virtual tapes are usually also much faster than many real tape drives. For a quick start, have a look at: Test environment with virtual tapes.

• Inexpensive installations: Without buying a tape drive you can enjoy the benefits of Amanda and backup to a bunch of harddisks. You can create CD/DVD-sized backups which you can burn onto optical disks later. Or you can backup to external disks connected with Firewire or USB.

• Disk-based installations: You can use the file driver to backup onto a set of virtual tapes hosted on a bunch of hard-disks or a RAID-system. Combined with another Amanda configuration that dumps the virtual tapes to real tapes, you can provide reliable backup with faster tapeless recovery. This is called "disk-to-disk-to-tape" backup by some people today.

Please be sure to understand the differences between holding disks and virtual tapes. The two serve different purposes; holding disks allow for parallelism of multiple disklist entries (DLE's) being backed up while virtual tapes are a replacement for physical tapes.

The virtual tapes are also called "vtapes" in this document.

Using Virtual Tapes

A virtual tape is implemented as a directory with a subdirectory named "data" in it.

# chown amanda:disk /amandatapes
# chmod 750 /amandatapes                       # backups contain secret files!
# su - amanda
$ mkdir -p /amandatapes/test/tape1/data

This tape can be manipulated by the ammt command, a replacement for the system command "mt". The ammt command understands the different output drivers from Amanda:

$ ammt -f file:/amandatapes/test/tape1 status
$ ammt -f file:/amandatapes/test/tape1 rewind

Vtapes are always non-rewinding. Just like Amanda needs them. That's why you always need to rewind it when you want to start reading a vtape from the beginning.

Basic writing to a vtape can be done with amdd, a replacement for the system command "dd". Virtual tapes have no real builtin capacity; the upper limit is "diskspace, the final frontier". However Amanda does obey the size you specify in tapetype definition of a vtape in amanda.conf. The amdd command also can specify an upperlimit on the virtual tapesize with the -l option:

$ amdd -l 200k if=/dev/urandom of=file:/amandatapes/test/tape1 bs=32k
amdd: write error: No space left on device
8+0 in
6+1 out

The above command writes 200 Kbytes of garbage (6 full blocks of 32k + 1 partial block) on the vtape before it bumps into the end of the virtual tape.

When there is no "data" subdirectory in a vtape, the vtape is "offline". You could burn the contents of the data directory to a CD-R, and store that away. When you want to read it, just mount is as a "data" directory, or even simpler, create a symlink "data" pointing to the mounted cdrom.

$ rm -r /amandatapes/test/tape1/data
$ ammt -f file:/amandatapes/test/tape1 status
file:/amandatapes/tape1: status: OFFLINE
$ ln -s /media/cdrom /amandatapes/test/tape1/data
$ ammt -f file:/amandatapes/test/tape1 status
file:/amandatapes/test/tape1: status: ONLINE

Amanda cannot backup a to CD-R, but can use it as a read protected vtape; making a backup to a vtape, and and later burning the contents of the data directory to a CD or DVD is the normal way.

See Also

• How To:Set Up Virtual Tapes

Credit

Based on text by: Stefan G. Weichinger, November - December, 2003 ; minor updates in April, 2005.