VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 5
Storage Checkpoints
What is a Storage Checkpoint?
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What is a Storage Checkpoint?
The VERITAS File System provides a unique Storage Checkpoint facility which 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 via a copy-on-write technique (see “How a Storage Checkpoint Works” on page 53). 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 which 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 56). 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) of the 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:
• 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.
• Multiple, read-only Storage Checkpoints 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 that have changed since the last Storage Checkpoint facilitates
backup and replication applications which 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 (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. Storage Checkpoint creation, however, may take several minutes to complete depending
on the number of files in the file system.