Technical data

Using BACKUP
11.3 Formulating a Backup Strategy
11.3 Formulating a Backup Strategy
When formulating a backup strategy, keep in mind the specific requirements of
your site and the advantages and disadvantages of the different types of backups.
Your backup strategy also depends on the following factors:
• The resources you can devote to backups
• The importance of the data
• The volatility of the data
For example, if you have a standalone workstation, a nightly image backup might
be your best approach.
Under other circumstances, you might want to choose some combination of
image and incremental backups. For example, daily image backups might be
inconvenient if your system always has interactive users logged in. You could
choose to perform a weekly image backup and nightly incremental backups.
Table 11–1 compares image and incremental backups.
Table 11–1 Comparison of Image and Incremental Backups
Backup Type Advantages Disadvantages
Image Faster to restore than
incremental backups. Backs
up entire disk.
Uses more space and time
than incremental backups.
Requires that no interactive
users are logged in because
of the effect on system
performance and because of
open file considerations (see
Section 11.15.1).
Incremental Takes less time and media
storage space.
More difficult to restore files.
Still requires periodic image
backups.
Notes
Before you perform an image backup, note the following items:
• The first time you back up a disk, you must perform an image backup
using the BACKUP/IMAGE/RECORD command before you perform
regular incremental backups. The image backup saves a copy of
the entire disk and marks each file as being saved. Subsequent
incremental backups assume that an image backup has been
performed; only new or modified files are saved.
If an image backup is not performed first, the incremental backups
save more files than might be necessary to ensure that an incremental
restore operation will be successful.
• If you perform an ANALYZE/DISK operation immediately after a
BACKUP/IMAGE restore operation of a disk, the system might
display a warning message similar to the following one:
%ANALDISK-W-ALLOCCLR, blocks incorrectly marked allocated
LBN 97 to 105, RVN 1
This can occur if you attempt to perform a BACKUP/IMAGE restore
operation where alias file entries are restored as separate (primary)
11–4 Using BACKUP