A snapshot file system is an exact image of a VxFS file system, referred to as the snapped file system, that provides a mechanism for making backups. The snapshot is a consistent view of the file system "snapped" at the point in time the snapshot is made. You can select files to back up from the snapshot using a standard utility such as cpio or cp, or back up the entire file system image using the vxdump or fscat utilities.
You use the mount command to create a snapshot file system; the mkfs command is not required. A snapshot file system is always read-only. A snapshot file system exists only as long as it and the snapped file system are mounted and ceases to exist when unmounted. A snapped file system cannot be unmounted until all of its snapshots are unmounted. Although it is possible to have multiple snapshots of a file system made at different times, it is not possible to make a snapshot of a snapshot.
A snapshot file system ceases to exist when unmounted. If mounted again, it is actually a fresh snapshot of the snapped file system. A snapshot file system must be unmounted before its dependent snapped file system can be unmounted. Neither the fuser command nor the mount command will indicate that a snapped file system cannot be unmounted because a snapshot of it exists.
On cluster file systems, snapshots can be created on any node in the cluster, and backup operations can be performed from that node. The snapshot of a cluster file system is accessible only on the node where it is created, that is, the snapshot file system itself cannot be cluster mounted.