8.4.2.4. The Advanced Maryland Automatic Network Disk Archiver (AMANDA)

AMANDA is a client/server based backup application produced by the University of Maryland. By having a client/server architecture, a single backup server (normally a fairly powerful system with a great deal of free space on fast disks and configured with the desired backup device) can back up many client systems, which need nothing more than the AMANDA client software.

This approach to backups makes a great deal of sense, as it concentrates those resources needed for backups in one system, instead of requiring additional hardware for every system requiring backup services. AMANDA's design also serves to centralize the administration of backups, making the system administrator's life that much easier.

The AMANDA server manages a pool of backup media and rotates usage through the pool in order to ensure that all backups are retained for the administrator-dictated retention period. All media is pre-formatted with data that allows AMANDA to detect whether the proper media is available or not. In addition, AMANDA can be interfaced with robotic media changing units, making it possible to completely automate backups.

AMANDA can use either tar or dump to do the actual backups (although under Red Hat Enterprise Linux using tar is preferable, due to the issues with dump raised in Section 8.4.2.3, “dump/restore: Not Recommended for Mounted File Systems!”). As such, AMANDA backups do not require AMANDA in order to restore files -- a decided plus.

In operation, AMANDA is normally scheduled to run once a day during the data center's backup window. The AMANDA server connects to the client systems and directs the clients to produce estimated sizes of the backups to be done. Once all the estimates are available, the server constructs a schedule, automatically determining the order in which systems are to be backed up.

Once the backups actually start, the data is sent over the network from the client to the server, where it is stored on a holding disk. Once a backup is complete, the server starts writing it out from the holding disk to the backup media. At the same time, other clients are sending their backups to the server for storage on the holding disk. This results in a continuous stream of data available for writing to the backup media. As backups are written to the backup media, they are deleted from the server's holding disk.

Once all backups have been completed, the system administrator is emailed a report outlining the status of the backups, making review easy and fast.

Should it be necessary to restore data, AMANDA contains a utility program that allows the operator to identify the file system, date, and file name(s). Once this is done, AMANDA identifies the correct backup media and then locates and restores the desired data. As stated earlier, AMANDA's design also makes it possible to restore data even without AMANDA's assistance, although identification of the correct media would be a slower, manual process.

This section has only touched upon the most basic AMANDA concepts. To do more research on AMANDA, start with the amanda(8) man page.