By default, Amanda writes one backup image per physical tape. It is possible to write more than one backup image per tape to improve tape utilization.
Amanda can delay the tape writes until a certain data size is reached in the staging area. The backed up data is stored in the backup staging area (Backup|staging). The backup images in the staging area can be restored and are part of the Amanda catalog.
To produce this behavior, the following Amanda configuration parameters may be manually added to the Amanda configuration file (/etc/amanda/<backup set name>/amanda.conf):
flush-threshold-dumped: Amanda will not begin writing data to a new volume until the amount of data on the staging area is at least this percentage of the volume size.
Example: flush-threshold-dumped 100 means that Amanda will flush the data from the staging area to the tape, only after the data accumulated in the staging area is at least 100 percent of the volume/tape size.
flush-threshold-scheduled: Amanda will not begin writing data to a new volume until the sum of the data on the staging area and the estimated amount of data remaining to be dumped during this run, is at least this percentage of the volume size.
Example: flush-threshold-scheduled 100 means that Amanda will flush the data from the staging area to the tape, only after the sum of the data that’s on the staging area and the estimated size of a backup that’s currently running (Amanda calculates this during the Estimate phase) is at least this percentage of the volume/tape size.
taperflush: At the end of a backup run, Amanda will start writing to a new tape, in order to flush the remaining data, if there is more data on the staging area at the end of a run.
Example: taperflush 100 means that Amanda will begin a new tape if the remaining data in the staging area is larger than this percentage of the volume/tape size.
- The Zmanda Management Console will not take these parameters into account and thus the required number of tapes for the Desired Retention Period (Advanced Options on the Backup|when page) will be higher than needed. It is up to the customer to ensure that enough tapes are in rotation for the Desired Retention Period.
- The staging area must be large enough to meet the threshold imposed by the above parameters, otherwise, due to lack of space, Amanda will disregard the threshold and write backup images to tape as usual.
- All these parameters are triggers that will determine when Amanda should flush the data from the staging area to the tape.
- If taperflush is greater than “0”, then the check box on the Backup|staging page to automatically flush backups on the next run must be checked.
- The complete information about these parameters, can be found in the man page of amanda.conf configuration file (See amanda.conf main page).