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

Chapter 5
Storage Checkpoints
Types of Storage Checkpoints
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Types of Storage Checkpoints
You can create the following types of Storage Checkpoints:
• Data Storage Checkpoints
• Nodata Storage Checkpoints
• Removable Storage Checkpoints
• Non-mountable Storage Checkpoints
Data Storage Checkpoints
A data Storage Checkpoint is a complete image of the file system at the time the Storage Checkpoint is
created. This type of Storage Checkpoint contains the file system metadata and file data blocks. You can
mount, access, and write to a data Storage Checkpoint just as you would to a file system. Data Storage
Checkpoints are useful for backup applications which require a consistent and stable image of an active file
system. Data Storage Checkpoints introduce some overhead to the system and to the application performing
the write operation. For best results, you can limit the life of data Storage Checkpoints to minimize the
impact on system resources.
Nodata Storage Checkpoints
A nodata Storage Checkpoint only contains file system metadata—no file data blocks. As the original file
system changes, the nodata Storage Checkpoint records the location of every changed block. Nodata Storage
Checkpoints use minimal system resources and have little impact on the performance of the file system
because the data itself does not have to be copied. Nodata Storage Checkpoints are useful with the Block
Level Incremental Backup feature.
Removable Storage Checkpoints
A removable Storage Checkpoint can “self-destruct” under certain conditions when the file system runs out of
space (see “Space Management Considerations” on page 64 for more information). After encountering certain
out-of-space (ENOSPC) conditions, the kernel removes Storage Checkpoints to free up space for the
application to continue running on the file system. In almost all situations, you should create Storage
Checkpoints with the removable attribute.
Non-mountable Storage Checkpoints
A non-mountable Storage Checkpoint cannot be mounted. You can use this type of Storage Checkpoint as a
security feature which prevents other applications from accessing the Storage Checkpoint and modifying it.