Generally speaking, the system administrator at each site should establish routine backup procedures for the entire system. Nonetheless, application programmers should know enough about these procedures to understand what is being backed up and with what frequency.
The administrator should design a backup strategy that suits the system’s needs and file usage patterns, after considering the tradeoffs between saving time on daily backups and losing time on a complicated restoration procedure. It should be remembered that complex backup procedures, when used by inexperienced operators, can sometimes result in loss of data.
This section suggests a few strategies and compares these tradeoffs to illustrate the advantages and drawbacks of each. The administrator may want to adopt one of these strategies just as it is, or use any of them as guidelines for determining the system’s backup strategy.
Full System Backup and the Incremental Cycle
In a full backup, all files, whether they have been accessed or not, are written out to backup media (as long as they do not have DX, DY, DCX or DCY in attribute 1 of the Account Definition item).
NOTE |
Rocket recommends that a full backup of the system be performed at least once a week, followed up by daily incremental backups. Full backups are kept indefinitely, so that it is possible at any future date to restore the system to its prior state as of any given week. |
An incremental backup saves only those changes made to the data since the last full backup. Daily incremental backups should be kept for at least seven days.
The table below outlines an example of a possible backup strategy. Ten sets of tapes are used over a two-week period, assuming a five-day work week.
Monday |
Tuesday |
Wednesday |
Thursday |
Friday |
Full filesave |
Incremental filesave |
Incremental filesave |
Incremental filesave |
Incremental filesave |
Tape set 1 |
Tape set 2 |
Tape set 3 |
Tape set 4 |
Tape set 5 |
Tape set 6 |
Tape set 7 |
Tape set 8 |
Tape set 9 |
Tape set 10 |
Make a full filesave of the entire data area on Monday.
Make an incremental filesave at the end of each succeeding day of the first week, which will back up all changes made since Monday.
Repeat this procedure over the course of the second week.
On Monday of the third week, make another full filesave using tape set 1.
On Tuesday make an incremental file- save using tape set 2. Repeat this procedure over the course of the third week. Thus, the backups always exist for the current week as well as for the preceding week.
For extra security, the administrator might make another full filesave at the end of each month, using a different set of backup media, and archive them for a year or more. Adding another weekly set of backup media (sets 11 through 15) ensures that backups fully cover the two weeks before the current week, as well as the current week’s backups.
NOTE |
Always perform a full filesave and verifications before upgrading the operating system or applications, and also before any end-of-year cleaning up of the system. Archive all backup media for later recovery. |
Daily Incremental Backups
Daily incremental backups are cumulative: that is, they include all changes made to the data since the last full backup. Thus, by the end of the week the daily backup is approaching the size of a weekly backup. This increases the time that each backup takes; however, it reduces the number of separate backups that need to be restored in the event of a system failure, since the latest daily backup is always inclusive.
Daily backups should be kept for at least seven days. Even though the daily backup from Thursday might include all files created or modified since the last weekly backup, it would not include a file that a user accidentally deleted on Wednesday. The user would need to go back to the Tuesday backup for that file.
Backing Up Individual Files or One Account
On a smaller system with only a few users, it might be desirable to have users back up their own important files using T-DUMP or S-DUMP whenever they log off or at whatever other interval seems appropriate to them.
In addition, a user may request the system administrator to back up a particular file or a single account. For example, when a particular project requiring a large number of related files is completed, those files might all be backed up and then removed from the system. Another user might request that all of his files be backed up at some particular checkpoint.
The following sections provide step-by-step instructions to perform each type of backup.
See Also