VFS Device
Introduction
Since release 2.4.3, Amanda supports the usage of a VFS Device, with prefix "file:".
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
- 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.
- 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.
- 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.
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
Credit
Based on text by: Stefan G. Weichinger, November - December, 2003 ; minor updates in April, 2005.