Information Technology Reference
In-Depth Information
up only the files that change during the previous increment period makes
backups much faster, but also makes full restores more complicated. For
example, assuming a daily incremental backup, a full restore would consist of
restoring the last full backup and all daily incremental backups.
The following sections describe several of the more commonly used backup
strategies. All are based on a full monthly backup once a month, performed
on the first day of the month. This discussion assumes that each backup
requires only one tape. This allows easy comparison of the number of tapes
required by each strategy.
Daily Cumulative/Weekly Cumulative Incremental Backups
The most commonly used backup strategy consists of a full backup per-
formed monthly (first day of the month). During the month (between full
backups), an incremental backup is performed each Friday that contains
everything changed since the last full backup (weekly cumulative). This pro-
vides intermediate data saves for restoring versions of files that might have
changed during the week. Similar incremental backups are performed
Monday through Thursday. Like the weekly cumulative backup, each back-
up of these backups contains everything changed since the last full backup
(daily cumulative). These allow quick restoration of a file that changed some-
time during the week that needs to be restored or full restoration of the sys-
tem by use of only two tapes.
This strategy requires one tape for the full backup, one tape for each week-
ly cumulative (four tapes), and either one tape for the daily cumulative back-
up or four (one for each day, Monday through Thursday), for a total of either
six or nine tapes. In terms of
ufsdump
levels, use 0 for the monthly backup, 9
for the daily, and 5 for the weekly.
Daily Incremental/Weekly Cumulative Backups
This backup strategy consists of a full backup performed monthly (1st day of
the month). During the month (between full backups), a backup is performed
each Friday that contains everything changed since the last full backup
(weekly cumulative). Each remaining day of the week, Monday through
Thursday, a discrete backup is performed. Each of these backups contains
everything that changed since the previous day's backup (daily incremental).
These allow quick restoration of a file that changed sometime during the
week that needs to be restored. Full restoration of the system would require
the last full backup, the latest weekly cumulative backup, and any daily dis-
crete backups. The main feature of this backup strategy is that the daily back-
ups are fast, because they only backup that day's changes.
