Saturday, January 10, 2009

AIX backup strategies

There are three types of backup methods:
1) Full backup
All the file are put into media during full backup.
The advantages are:
  • Restoring from a full backup lowers the tape handling activities compared to an incremental or differential backup.
  • The content from media is from within the same backup window (rollback and redundancy)

The disadvantages are

  • The backup window is wide.
  • if the data does not change, every full backup media contain the same data.

2) Differential backup

The diffrential backup strategy first look for the modification time of file and comparre it with the last full backup time. Differential backup are clumative; once a file has been modified, it may be included in every differential backup untill the next full backup.

The advantages are

  • To restore, the latest full backup and only the latest differential backup media sets are needed.
  • The backup window is smaller than a full backup.

The disadvantages are

  • If data changes a lot between full backups, the data to back up tends to grow a bit over time, using more media.
3) Incremental backup

Incremental backups are similar to differential backups in that both back up only modified files.
Incremental backup checks the difference between the modification time of a file and the last backup time (either being full or incremental backup). If the modification date is more recent than the last backup date, the file is backed up.

The advantages are
  • The backup window is smaller than a full backup.
  • Only the differences from a previous backup will be written on media.

The disadvantages are

  • To restore, the latest full backup and all the subsequent incremental backup
    media sets following that full backup are needed.
  • To restore a single file, tape handling operations are intensive.
  • A damaged or lost media in the incremental set can mean disaster: The
    modifications of those files on that media may be lost forever.
Both incremental and differential backups are used in conjunction with regularly scheduled full backups.

How to take backup of AIX System

The mksysb command create a bootable image of all mounted file systems on the rootvg volume group. The root volume group image is in backup file format, starting with data files and then any optional map files. The image file contains information describing the image installed during the BOS installation process. This information includes the names, sizes, maps and mount points of logical volumes and file systems in the rootvg. Command to take backup of aix operating system in tape drive is
mksysb -e /dev/rmt0.