Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

only the name space (directory hierarchy) of the file system, but also the user data
as it existed at the moment the file system image was captured.
You can use a Storage checkpoint in many ways. For example, you can use them
to:
■ Create a stable image of the file system that can be backed up to tape.
■ Provide a mounted, on-disk backup of the file system so that end users can
restore their own files in the event of accidental deletion. This is especially
useful in a home directory, engineering, or email environment.
■ Create a copy of an application's binaries before installing a patch to allow for
rollback in case of problems.
■ Create an on-disk backup of the file system in that can be used in addition to
a traditional tape-based backup to provide faster backup and restore
capabilities.
■ Test new software on a point-in-time image of the primary fileset without
jeopardizing the live data in the current primary fileset by mounting the
Storage Checkpoints as writable.
Storage Foundation Cluster File System backup
strategies
The same backup strategies used for standard VxFS can be used with SFCFS
because the APIs and commands for accessing the namespace are the same. File
System checkpoints provide an on-disk, point-in-time copy of the file system.
Because performance characteristics of a checkpointed file system are better in
certain I/O patterns, they are recommended over file system snapshots (described
below) for obtaining a frozen image of the cluster file system.
File System snapshots are another method of a file system on-disk frozen image.
The frozen image is non-persistent, in contrast to the checkpoint feature. A
snapshot can be accessed as a read-only mounted file system to perform efficient
online backups of the file system. Snapshots implement “copy-on-write” semantics
that incrementally copy data blocks when they are overwritten on the snapped
file system. Snapshots for cluster file systems extend the same copy-on-write
mechanism for the I/O originating from any cluster node.
Mounting a snapshot filesystem for backups increases the load on the system
because of the resources used to perform copy-on-writes and to read data blocks
from the snapshot. In this situation, cluster snapshots can be used to do off-host
backups. Off-host backups reduce the load of a backup application from the
primary server. Overhead from remote snapshots is small when compared to
Storage Foundation Cluster File System architecture
Storage Foundation Cluster File System backup strategies
26