Sun Microsystems 5310 NAS manual Checkpoint Lifecycle, Checkpoint Creation

6.1.2Checkpoint Lifecycle

Checkpoints are created and managed using the fs_chkpntcl( ) function of filesystem which is sfs2_chkpntctl( ) for SFS2 filesystem. The checkpoint management interfaces use this call to create, delete and deactivate checkpoints and checkpointing on sfs2 filesystems.

Checkpoints have three states:

■Active: while checkpoints are active, they can be accessed for most of the read- only file system operations.

■Delete pending: when a checkpoint has expired and automatically removed by the system or users explicitly remove them, they are marked as "delete pending." Later, one of the file system workers (or threads) called checkpoint cleaner will actually remove it. When a checkpoint status is changed from active, it will no longer be accessible and a new checkpoint with the same name can be created.

■Deleting: while the checkpoint cleaner is removing a checkpoint, its state is deleting.

6.1.2.1Checkpoint Creation

There is a special mode page for checkpointing that is like a directory and contains all of the information about checkpoints on an sfs2 filesystem. The address of this page is in the volume label of the SFS2 filesystem. It is allocated when checkpoints are active on an SFS2 filesystem.

This page contains a table of active checkpoints on filesystem, properties of checkpoints (whether they are visible or not…) and also an array of pointers which are the first of a three-level indirection to pages containing the mappings for the LFS blocks. (The mappings are described in the next section.) There is also a stack of active checkpoints. Each checkpoint that is created will be pushed on top of the stack. When creating a checkpoint, the sfs2cp_dirop( ) function is called by the sfs2_chkpntctl( ) function. This function creates a checkpoint in the checkpoint pseudo-directory.

Chapter 6 Checkpoints/Snapshots 6-3