Storix Software SBAdmin User Guide - Manual (Page 62)

The software is installed with sample script programs that may be used for any client or server pre-backup,
post-backup or pre/post snapshot program. The programs are called “prepost.sample” and
"prepostsnap.sample" and will simply display the values of all of the above variables when the backup job
is run. You may edit or view the contents of this script file (contained in the DATADIR/custom directory),
which contains additional details on the use of this option.
Incremental/Differential Backups
An incremental backup is one in which the only data to be included in the backup is that which has changed
since the prior incremental backup level. An incremental backup level can be from 0 to 9, where 0 is a “full
incremental” backup from which all other levels are based. Levels 1 through 9 indicate that only data that has
changed since the last prior-level backup should be included.
Differential backups are also incremental backups, except that backups include a cumulative list of files that
have changed since a certain time. This is achieved by running the same incremental level backup repeatedly,
backing up the same files that changed since the last prior-level (or level 0) backup along with any additional
files that have changed since the last time the same incremental level backup was run. The result is that the
backup gets continually larger each time it is run, until a prior level (or level 0) backup is run again.
Raw devices such as logical volumes (AIX) and other partitions (slices or ZFS volumes on Solaris, meta-disks
on Solaris & Linux, etc) that do NOT contain mounted filesystems will always be backed up in their entirety if
they have been written to since the last backup of a prior level. This assumes that you selected to “Include as
raw data” this information in the backup profile. If included, we assume these raw devices will be included with
the backups as well as the “files”.
Incremental Backup Examples
1. Consider the following backup schedule:
Monday Level 0
Tuesday Level 1
Wednesday Level 2
Thursday Level 3
Friday Level 4
a. On Monday, all of the data in the specified filesystem or volume group will be backed up, and the
volume group or the next level of backups will be based.
b. On Tuesday, only the files or logical volumes that have changed since Monday’s backup will be
included in the incremental level 1 backup.
c. On Wednesday, only files backed up since the last prior-level backup (level 1) will be included in
this backup.
d. Likewise on Thursday and Friday.
e. On the following Monday, a new incremental level 0 is performed, backing up all data once again.
This is the new backup from which all subsequent backups will be based. Any incremental backups
performed prior to this level 0 will be considered obsolete.
2. In a second example, consider the following backup schedule, which is often referred to as differential
backups since we’re effectively backing up the differences between a filesystem now versus a specific
day in the past :
First day of the Month Level 0
Each Friday night
Level 4
Each other weekday Level 7
Storix System Backup Administrator 62 Version 8.2 User Guide