Overview of Snapshots
A snapshot is a read-only copy of a volume. Snapshots can be created almost instantly, and they initially consume no additional disk space within the pool. However, as data within the active dataset changes, the snapshot consumes disk space by continuing to reference the old data, thus preventing the disk space from being freed.
Snapshots include the following features:
The persist across system reboots.
The theoretical maximum number of snapshots is 264.
Snapshots use no separate backing store. Snapshots consume disk space directly from the same storage pool as the file system or volume from which they were created.
Recursive snapshots are created quickly as one atomic operation. The snapshots are created together (all at once) or not created at all. The benefit of atomic snapshot operations is that the snapshot data is always taken at one consistent time, even across descendent file systems.
Snapshots of volumes cannot be accessed directly, but they can be cloned, rolled back to, and so on.