Archiving and Recovery

Information in file store can be lost through hardware or software failures : Hence, the need for Backup and Recovery (usually to magnetic tape, Digital Audio Tape (DAT) or CD-ROM).

• Periodic (total) Dump : Copy everything in file store.
  File system may be very large : time consuming - there may not be that many changes between the periods being considered.
  Recovery of individual files by scanning entire dump tape
• Incremental Dump : Only copy files updated, changed or created since last dump
  Using flags per file or per directory to determine files which need to be saved
  Dump program usually run as a low priority process and clears flags associated with files or directories
• Must be performed frequently to avoid loss of data (could generate a large number of dump tapes)

Recovery:

• Involves working backwards through incremental dump tapes
• Restore any dumped files except those already restored (overwriting with old copies!!)
• Finally use last periodic dump

this is better than working forwards - WHY ?