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 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
Preparing to Back Up User Disks).
Incremental
Takes less time and media
storage space.
More difficult to restore files. Still requires
periodic image backups.
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:
This can occur if you attempt to perform a BACKUP/IMAGE restore
operation where alias file entries are restored as separate (primary)
file entries. (The primary file, which uses the same file header
but allocates different data storage blocks, is also restored.) However, despite the error message, note that there is no
BACKUP error or loss of data.
You do not have to change tapes or disks during a backup if
any of the following statements is true:
All of the files fit on a single piece
of storage media.
Your site uses a tape loader.
You have several disk or tape drives available.
In these cases, the backup can be performed by a batch job
that runs late at night or at some other time when interactive use
of the system is likely to be at a minimum.
Backing Up Your Workstation Disk contains some sample command procedures
that you can run in a batch job to back up your disks.
HP OpenVMS System Manager's Manual, Volume 1:... 
Using BACKUP
