Snapshot and Direct I/O Descriptions

Introducing Arcserve Backup Agents and Options › Using Agents › Client Agent › Adding and Configuring the Client Agents › UNIX, Linux, and Mac OS X Client Agent Configuration › Snapshot and Direct I/O Support (UNIX Only) › Snapshot and Direct I/O Descriptions

With Direct I/O, the client agent takes a snapshot on advanced versions of VxFS, Online JFS (HP-UX), and UFS with fssnap installed on Solaris. The client agent mounts the snapshot to a temporary directory created in the root volume, and then generates the snapshot backup. After the snapshot backup is complete, the client agent dismounts from the temporary directory and deletes the snapshot.

To perform a snapshot backup, you must specify a snapshot buffer. A snapshot buffer is the disk space used to store the original data before it is overwritten in the snapped volume. Remember these considerations when using the snapshot buffer:

The snapshot buffer needs to be large enough to store all the data that changes in the snapped volume for the duration of the backup. If the snapshot buffer runs out of space, the snapshot becomes invalid and the backup fails.
The snapped volume and the snapshot buffer should not be on the same file system.
For better performance, the snapped volume and the snapshot buffer should be on separate physical disks.
For UFS on the Solaris platform (using fssnap), the snapshot buffer can be a file name, a directory name, or a raw partition.

For a Direct I/O backup or restore, you need to check the client environment and edit the caagperf.cfg configuration file. You can view Snapshot and Direct I/O on the file systems in the caagperf.cfg file by executing the mount command at the command line after submitting the backup or restore job.

For Snapshot, the output that appears after executing the mount command is a new, read-only file system with the mount point starting with the prefix SNAP_HOME_ . A Direct I/O user can observe the changes in the mount options on that particular file system. You can also see the detailed messages in the caagperf.log file if you enabled the logging flag in the caagperf.cfg file.

The following sections describe how to configure a UNIX client agent to use these features.