System Administration Guide: Basic Administration

Why Use UFS Snapshots?

UFS snapshots enables you to keep the file system mounted and the system in multiuser mode during backups. Previously, you were advised to bring the system to single-user mode to keep the file system inactive when you used the ufsdump command to perform backups. You can also use additional Solaris backup commands like tar and cpio to back up a UFS snapshot for more reliable backups.

The fssnap command gives administrators of non-enterprise-level systems the power of enterprise-level tools like Sun StorEdgeTM Instant Image without the large storage demands.

UFS snapshots is similar to the Instant Image product. Instant Image allocates space equal to the size of the entire file system that is being captured. However, the backing-store file that is created by UFS snapshots occupies only as much disk space as needed, and you can place a maximum size on the backing-store file.

This table describes specific differences between UFS snapshots and Instant Image.

UFS Snapshots 

Instant Image 

Size of the backing-store file depends on how much data has changed since the snapshot was taken 

Size of the backing-store file equivalent equals the size of the entire file system being copied 

Does not persist across system reboots 

Persists across system reboots 

Works on UFS file systems 

Cannot be used with root (/) or /usr file systems

Part of the Solaris 8 1/01, 4/01, 7/01, 10/01, and 10/02 releases and the Solaris 9 release 

Part of Sun StorEdge products 

Although UFS snapshots can make copies of large file systems, Instant Image is better suited for enterprise-level systems. UFS snapshots is better suited for smaller systems.