Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Storage Checkpoints
What is Storage Checkpoint ?
Chapter 574
What is Storage Checkpoint ?
VERITAS File System provides a unique Storage Checkpoint facility that quickly creates a persistent image
of a file system at an exact point in time. Storage Checkpoints significantly reduce I/O overhead by
identifying and maintaining only the file system blocks that have changed since the last Storage Checkpoint
or backup through a copy-on-write technique (See “How a Storage Checkpoint Works” on page 76). Unlike
a disk-based mirroring technology that requires a separate storage space, this VERITAS technology
minimizes the use of disk space by creating a Storage Checkpoint within the same free space available to the
file system.
Storage Checkpoints are data objects that are managed and controlled by the file system. As a result, Storage
Checkpoints are persistent across system reboots and crashes.You can create, remove, and rename Storage
Checkpoints because they are data objects with associated names(See “Storage Checkpoint Administration”
on page 81).After you create a Storage Checkpoint of a mounted file system, you can also continue to create,
remove, and update files on the file system without affecting the logical image of the Storage Checkpoint.
This technology preserves not only the name space (directory hierarchy) ofthe file system, but also the user
data as it existed at the moment the Storage Checkpoint was taken.
Storage Checkpoints differ from VERITAS File System snapshots in the following ways because they:
• Allow write operations to the Storage Checkpoint itself.
• Persist after a system reboot or failure.
• Share the same pool of free space as the file system.
• Maintain a relationship with other Storage Checkpoints by identifying changed file blocks since the last
Storage Checkpoint.
• 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.
Various backup and replication solutions can take advantage of Storage Checkpoints. The ability of Storage
Checkpoints to track the file system blocks, which have changed since the last Storage Checkpoint,
facilitates backup and replication applications that 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 (for example, 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.