Using the VxFS file change log for incremental backups property

The Use VxFS file change log feature is supported on all platforms and versions where VxFS file systems support FCL.

The following VxFS file systems support FCL:

Solaris SPARC platform running VxFS 4.1 or greater
AIX running VxFS 5.0 or greater.
HP 11.23 running VxFS 5.0 or greater.
Linux running VxFS 4.1 or greater

The File Change Log (FCL) tracks changes to files and directories in a file system. Changes can include files created, links and unlinks, files renamed, data that is appended, data that is overwritten, data that is truncated, extended attribute modifications, holes punched, and file property updates.

NetBackup can use the FCL to determine which files to select for incremental backups, which can potentially save unnecessary file system processing time. The FCL information that is stored on each client includes the backup type, the FCL offset, and the timestamp for each backup.

The advantages of this property depend largely on the number of file system changes relative to the file system size. The performance impact of incremental backups ranges from many times faster or slower, depending on file system size and use patterns.

For example, enable this property for a client on a very large file system that experiences relatively few changes. The incremental backups for the client may complete sooner since the policy needs to read only the FCL to determine what needs to be backed up on the client.

If a file experiences many changes or multiple changes to many files, the time saving benefit may not be as great.

See About the Backup Selections tab.

The following items must be in place for the Use VxFS file change log feature to work:

Enable the Use VxFS file change log property for every client that wants NetBackup to take advantage of the FCL.
Enable the FCL on the VxFS client.

See the Veritas File System Administrator's Guide for information about how to enable the FCL on the VxFS client.
Enable the Use VxFS file change log property on the client(s) in time for the first full backup. Subsequent incremental backups need this full backup to stay synchronized.
Specify the VxFS mount point in the policy backup selections list in some manner:
- By specifying ALL_LOCAL_DRIVES.
- By specifying the actual VxFS mount point.
- By specifying a directory at a higher level than the VxFS mount point, provided that Cross mount points is enabled.
  
  See Cross mount points policy attribute.

If the policy has Collect true image restore information or Collect true image restore information with move detection enabled, it ignores the Use VxFS file change log property on the client.

Additional information about the VxFS file change log feature:

Activity Monitor messages

The Activity Monitor displays any messages that note when the file change log is used during a backup as follows:
```
Using VxFS File Change Log for backup of pathname
```
The Activity Monitor also notes when full and incremental backups are not synchronized.
Keeping the data files synchronized with the FCL

The data files must be in sync with the FCL for this property to work. To keep the data files synchronized with the FCL, do not turn the FCL on the VxFS client off and on.

Note:

If NetBackup encounters any errors as it processes the FCL, it switches to the normal files system scan. If this switch occurs, it appears in the Activity Monitor.
VxFS administration

Additional VxFS commands are available to administrate the FCL in the Veritas File System Administrator's Guide.