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

Chapter 5

Storage Checkpoints

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 multiple file system

Storage Checkpoint simultaneously freezes the file systems, creates a Storage Checkpoint on all 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.

Figure 5-1 Primary Fileset and Its Storage Checkpoint

Primary Fileset

Storage Checkpoint

/database

emp.db jun.dbf emp.db jun.dbf

/database