Overview of ZFS Snapshots
A snapshot is a read-only copy of a file system or 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.
A clone is a writable volume or file system whose initial contents are the same as the dataset from which it was created. Clones can be created only from a snapshot.
ZFS snapshots include the following features:
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They persist across system reboots.
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The theoretical maximum number of snapshots is 264.
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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.
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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 descendant file systems.
Snapshots of volumes cannot be accessed directly, but they can be cloned, backed up, rolled back to, and so on. For information about backing up a ZFS snapshot, see Saving, Sending, and Receiving ZFS Data.
This section covers the following topics:
Note:
Certain snapshot operations can be set by using the Desktop's Time Slider. See Using Time Slider.