Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

■ Can have multiple, read-only Storage Checkpoints that reduce I/O operations
and required storage space because the most recent Storage Checkpoint is the
only one that accumulates updates from the primary file system.
■ Can restore the file system to its state at the time that the Storage Checkpoint
was taken.
Various backup and replication solutions can take advantage of Storage
Checkpoints. The ability of Storage Checkpoints to track the file system blocks
that have changed since the last Storage Checkpoint facilitates backup and
replication applications that only need to retrieve the changed data. Storage
Checkpoints significantly minimize data movement and may promote higher
availability and data integrity by increasing the frequency of backup and
replication solutions.
Storage Checkpoints can be taken in environments with a large number of files,
such as file servers with millions of files, with little adverse impact on performance.
Because the file system does not remain frozen during Storage Checkpoint creation,
applications can access the file system even while the Storage Checkpoint is taken.
However, Storage Checkpoint creation may take several minutes to complete
depending on the number of files in the file system.
Operation of a Storage Checkpoint
The Storage Checkpoint facility freezes the mounted file system (known as the
primary fileset), initializes the Storage Checkpoint, and thaws the file system.
Specifically, the file system is first brought to a stable state where all of its data
is written to disk, and the freezing process momentarily blocks all I/O operations
to the file system. A Storage Checkpoint is then created without any actual data;
the Storage Checkpoint instead points to the block map of the primary fileset.
The thawing process that follows restarts I/O operations to the file system.
You can create a Storage Checkpoint on a single file system or a list of file systems.
A Storage Checkpoint of multiple file systems simultaneously freezes the file
systems, creates a Storage Checkpoint on all of the file systems, and thaws the
file systems. As a result, the Storage Checkpoints for multiple file systems have
the same creation timestamp. The Storage Checkpoint facility guarantees that
multiple file system Storage Checkpoints are created on all or none of the specified
file systems, unless there is a system crash while the operation is in progress.
Note: The calling application is responsible for cleaning up Storage Checkpoints
after a system crash.
269Administering Storage Checkpoints
Operation of a Storage Checkpoint