Amanda:Why does Amanda not append to a tape?

From The Open Source Backup Wiki (Amanda, MySQL Backup, BackupPC)

Jump to: navigation, search

This article answers a FAQ (frequently asked question).

This question is most often asked by individual computer users as a cost consideration.

Amanda was developed at the University of Maryland Computing Center for use in moderately sized computer centers. That it can be used by users of small computers is a testament to its designers and maintainers.

While it may seem cost effective to put as many dumps as possible on a single tape, in a computing center that would be considered a very risky decision. The loss of, or damage to, a single tape would be the loss of many days worth of dumps. That is too much to chance.

Thus, Amanda was designed to never overwrite a non-Amanda tape, nor an Amanda tape from a different configuration, nor an Amanda tape from the current configuration that is still "active", i.e. has backups on the tape more recent than the dumpcycle length.

If you still feel you want Amanda to put multiple dumps on a single tape, there is a crude way to accomplish your goal - see below. But first ask yourself, "If my data is worth so little that I can not afford a few more tapes, why am I backing it up?"

NOTE: Most of the time it won't be YOU paying for the tapes as you may be working for some company. If your boss tries to force you into doing this multiple-dumps-on-one-tape thing, be sure to point him at this risk. Business people tend to understand the price-difference between some tapes and a major data-loss. --Stefan G. Weichinger

Improving tape utilization

Amanda 2.6 and later releases

You can use "taperflush", "flush-threshold-dumped" and "flush-threshold-scheduled" to improve tape utilization close to 100%. See amanda.conf(5) configuration file for more information on these parameters. Multiple backup images will be backed up to a single tape. This method requires holding disk space to be at least one tape length and size of the backup in progress.

"autoflush" parameter should be set to "yes", if Amanda amdump(5) command should flush prior and current backup image.

During amdump run, flush-threshold-scheduled and flush-threshold-dumped determine if the taper can start writing to a new tape. At the end of a run, taperflush is used to determine if the taper can start writing to anew tape.

flush-threshold-dumped        100 
flush-threshold-scheduled     100 
taperflush                    100
autoflush                     yes

Above parameters will attempt to maximize tape utilization and leave the backup images on the holding disk after amdump run.

Older releases (Amanda 2.5.x and earlier)

A common way to put multiple dumps on a single tape is to let them accumulate on the holding disk and use the amflush(8) command when you want to put them on tape. I.e. if you want a weeks' worth of backups on a single tape, leave the tape out for a week. Then stick it in and run amflush.

(Better make sure you have sufficient disk space on your holding disk.)

Note, a slight variant of this is to have the parameter autoflush in amanda.conf(5) set to "yes". (Users of older Amanda-releases should check out if their version already supports that parameter.)

Then after several dumps have collected in the holding disk, put the tape in before that day's amdump is scheduled. amdump will both flush the holding disk to tape and add the regularly scheduled dump.

(provided by Jon LaBadie; original version at http://www.amanda.org/docs/topten.html#id348056)

Personal tools