back up and recovery

back up and recovery

1. backup refers to making copies of data that may be used to restore original data if loss occurs

   • to avoid perm data loss and ensure data integrity

2. restoring files to their original state before failure occured is called recovery

3. BACK UP REQUIREMENTS

   • Loss may occur due to:
     • hardware fault such as hard disk crash
       • accidental deleting of files
         • natural disaster
           • deliberate action; sabotage or terrorism
             • aspects to be considered:
               • WHAT is to be backed up
                 • WHEN is the best time to back up
                   • HOW the backup should be carried out
                     • WHAT MEDIA used to store data
                       • WHOSE RESPONABILITY to monitor and maintain backup
                   • for systems that work through the day backup occurs at night
                     • some softwares can automatically backup but backup tapes are changed everyday
                       • back-up log should be kept; details of time, date, medium with name of person who carried it out

4. BACK UP

   • OS needs suitable backup as is extremely important
     • applications from CD-ROMS are usually customised once installed without backup this would be lost

5. FULL BACKUP

   • Image of the system is copied to a storage medium such as a tape everyday ( so can be restored by just one tape)
     • for small servers which are not in 24/7 use
       • can take considerably long to carry out
         • if system is running at the same time it is likely to slow down processing

6. DIFFERENTIAL BACKUP

   • only backs up files that are different from the full backup or after updates
     • uses just two tapes
       • when time elasped from last backup of changes will be time consuming
         • SMALL - MEDIUM ORG.

7. INCREMENTAL BACKUP

   • backs up all files that have changed since the last backup tape
     • less time to backup
       • may take long time to restore as several tapes are used
         • e.g. diff tape for each night of backup
           • need for transaction log
             • which must be backed up as well
               • SMALL - MEDIUM ORG.

8. ONLINE BACKUP

   • DISK MIRRORING
     • storing identical data on two diff disks
       • RAID - Redundant array of inexpensive disks
         • fault torrent system which uses a set of two+ disk drives; fault less likely to occur

9. REMOTE BACKUP

   • Transfer files to a remote site using wide area network
     • data is vunerable and will need encrypting

10. RESPONSIBILITY

    • Should be allocated to specific employee
      • their job to ensure all is backed up and copies in safe place
        • their job to ensure recovery procedures are practised
          • careful checks to ensure back up works
            • recording and playback equiptment is compatible

11. Backup for batch processing

    • common method when there are large numbers of similar transactions
      • e.g. when processing systems such as payroll or utlitiy billing
        • all data is input and collected together and processed in a single operation
          • sometimes entered offline into a transaction file
            • merged with corresponding records of the master file in a new master file
              • old= farther file and new=son
                • if son corrupted then farther can restore
                  • in all other processing modes except batch data is over written as transaction occurs so backup copies must be made