Veritas™ File System 5.0.1 Administrator's Guide

application running an online transaction processing (OLTP) workload on a
snapped file system was measured at about 15 to 20 percent slower than a file
system that was not snapped.
Differences Between Snapshots and Storage
Checkpoints
While snapshots and Storage Checkpoints both create a point-in-time image of a
file system and only the changed data blocks are updated, there are significant
differences between the two technologies:
Table 5-1
Differences between snapshots and Storage Checkpoints
Storage CheckpointsSnapshots
Reside on the same device as the
original file system
Require a separate device for
storage
Can be read-only or read-writeAre read-only
Are persistentAre transient
Can exist and be mounted on their ownCease to exist after being
unmounted
Track changed blocks on each file in
the file system
Track changed blocks on the file
system level
Storage Checkpoints also serve as the enabling technology for two other Veritas
features: Block-Level Incremental Backups and Storage Rollback, which are used
extensively for backing up databases.
See “About Storage Checkpoints” on page 83.
About snapshot file system disk structure
A snapshot file system consists of:
■ A super-block
■ A bitmap
■ A blockmap
■ Data blocks copied from the snapped file system
The following figure shows the disk structure of a snapshot file system.
79Online backup using file system snapshots
Differences Between Snapshots and Storage Checkpoints