vob_snapshot

The file /var/adm/rational/clearcase/config/snapshot.conf stores information used to notify interested parties of VOB database snapshot activity on a particular host. Here are the parameters in snapshot.conf and their default values:

When vob_snapshot runs on a VOB host, it checks each locally stored VOB for the existence of a multipart string attribute that specifies snapshot parameters. An administrator uses the vob_snapshot_setup utility to apply the vob_snapshot_parameters attribute to each VOB or replica for which snapshots will be taken. The individual components of the attribute string specify the following:

• Where to put the VOB database snapshot

  A disk location to store the snapshot. Typically, this location is backed up later (along with the VOB storage directory as part of normal backup operations), and it is overwritten by the next snapshot.

• Whether to run db_check on the VOB database snapshot

  The db_check utility performs fundamental database consistency and integrity checks. (Later, at recover time, checkvob may examine the VOB database for ClearCase anomalies.) The db_check pass occurs after all snapshots are complete on the local host.

• UNIX and Linux only—Which users to notify (receive mail) about snapshot operations on this VOB

  A list of user names to be notified when vob_snapshot processes this VOB. This per-VOB list supplements the per-host notification list maintained in /var/adm/rational/clearcase/config/snapshot.conf. The snapshot.conf file also specifies the notification program to be used.

For more information about setting these parameters for a particular VOB, see vob_snapshot_setup.

When vob_snapshot encounters a VOB that is configured for database snapshot, it performs the following steps (logging messages in the snapshot_log (UNIX and Linux) or ccase-home-dir\var\log\snap_log (Windows) file along the way):

1. Verifies that the snapshot target directory exists and is writable.
2. Locks the VOB. If vob_snapshot cannot lock the VOB, it proceeds with the snapshot, but logs the snapshot's status as questionable.
3. Checks the VOB's specified snapshot target directory for sufficient disk space.
4. Creates a subdirectory whose name is the VOB's replica UUID. If a directory with that name already exists, remove it first (that is, remove the previous snapshot).
5. Copies the VOB database directory tree to the subdirectory created in Step 3
6. Unlocks the VOB.
7. Repeats Step 1 through Step 6 for the next VOB.
8. Runs db_check on all VOBs configured for this check.
   Note: If the log or UNIX or Linux notification mail reveals a failed db_check, check the log for obvious errors. If you cannot resolve the problem, contact IBM Software Support for Rational products.
9. (UNIX and Linux) Sends mail to per VOB and per host notification lists.

You must lock the VOB and back up the entire VOB storage directory (and any remote UNIX or Linux storage pools). Such a backup avoids the issue of skew between VOB database snapshot and VOB storage pools (which are typically backed up some time after the snapshot), but it requires that the VOB remain locked during the entire backup operation.