VERITAS File System 4.1 Administrator's Guide

Storage Checkpoints
How a Storage Checkpoint Works
Chapter 592
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.