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

Storage Checkpoints
How a Storage Checkpoint Works
Chapter 576
How a Storage Checkpoint Works
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 (described below) 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.
As mentioned above, a Storage Checkpoint of the primary fileset initially contains a pointer to the file
system block map rather than to any actual data. The block map points to the data on the primary fileset. The
figure below shows the file system /database and its Storage Checkpoint. The Storage Checkpoint is
logically identical to the primary fileset when the Storage Checkpoint is created, but it does not contain any
actual data blocks.