VERITAS File System 4.1 Administrator's Guide

Online Backup Using File System Snapshots
Differences Between Snapshots and Storage Checkpoints
Chapter 6 123
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:
• Snapshots require a separate device for storage. Storage Checkpoints reside on the same
device as the original file system.
• Snapshots are read-only. Storage Checkpoints can be read-only or read-write.
• Snapshots are transient. Storage Checkpoints are persistent.
• Snapshots cease to exist after being unmounted. Storage Checkpoints can exist and be
mounted on their own.
• Snapshots track changed blocks on the file system level. Storage Checkpoints track
changed blocks on each file in the file system.
• Although there can be more than one snapshot of a file system, they are all based on
a single, parent file system. Storage Checkpoints can be based on other Storage
Checkpoints.
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 Chapter 5, “Storage Checkpoints,” on page 89 for more
information.