Journal-based backup

Journal-based backup is an alternate method of backup that uses a change journal maintained by the IBM Spectrum Protect journal service process.

Journal-based backup is supported for all Windows clients.

To support journal-based backup, you must configure the journal engine service using the dsmcutil command or the client GUI setup wizard.

A backup for a particular file system will be journal-based when the IBM Spectrum Protect journal service has been installed and configured to journal the particular file system, and a valid journal has been established for the file system.

The primary difference between traditional incremental backup and journal-based backup is the method used for backup and expiration candidates.

Traditional incremental backup obtains the list of backup and expiration candidates by building comprehensive lists of local objects, and lists of active server objects for the file system being backed up. The local lists are obtained by scanning the entire local file system. The server list is obtained by querying the entire server inventory for all active objects.

The two lists are compared, and candidates are selected according to the following criteria:

• An object is selected as a backup candidate if it exists in the local list. but doesn't exist in the server list. The object is also a backup candidate if it exists in both lists, but differs according to incremental criteria (for example, attribute changes, date and size changes).
• An object is selected as an expiration candidate if it exists in the server list, but doesn't exist in the local list.

Journal-based backup obtains the candidates list of objects to backup and expire by querying the journal service for the contents of the change journal of the file system being backed up.

Change journal entries are cleared (marked as free) after they have been processed by the backup client and committed on the IBM Spectrum Protect server.

Journal-based backup is activated by configuring the journal service to monitor specified file systems for change activity.

Journal-based backup is enabled by successfully completing a full incremental backup.

The journal engine service does not record changes in specific system files, such as the registry, in the journal. Therefore, a journal-based backup will not back up this file. See the journal service configuration file, tsmjbbd.ini, in the client installation directory for excluded system files.

You can use journal-based backup when backing up file systems with small or moderate amounts of change activity between backup cycles. If you have many file changes between backup cycles, you will have very large change journals. Many changes to the journal-based backup file might pose memory and performance problems that can negate the benefits of journal-based backup. For example, creating, deleting, renaming, or moving very large directory trees can also negate the benefit of using journal-based backup instead of normal incremental backup.

Journal-based backup is not intended to be a complete replacement for traditional incremental backup. You should supplement journal-based backup with a full progressive incremental backup on a regular basis. For example, perform journal-based backups on a daily basis, and full incremental backups on a weekly basis.

Journal-based backup has the following limitations:

• Individual server attributes are not available during a journal-based backup. Certain policy settings such as copy frequency and copy mode might not be enforced.
• Other operating-system specific behaviors might prevent objects from being processed properly. Other software that changes the default behavior of the file system might prevent file system changes from being detected.
• If the file system is very active when a journal-based backup is in progress, it is possible that a small number of deleted files will not be expired.
• If you restore files to a file system that has an active journal, some of the restored files might get backed up again when the next journal-based backup occurs, even if the files have not changed since they were restored.