Solaris

Snapshots
A snapshot is a read-only copy of a file system or volume.
Snapshots can be created extremely quickly, and initially
consume no additional space within the pool. As data within
the active dataset changes, the snapshot consumes more data
than would otherwise be shared with the active dataset.

Snapshots can have arbitrary names. Snapshots of volumes can
be cloned or rolled back, but cannot be accessed indepen-
dently.

File system snapshots can be accessed under the
".zfs/snapshot" directory in the root of the file system.
Snapshots are automatically mounted on demand and may be
unmounted at regular intervals. The visibility of the ".zfs"
directory can be controlled by the "snapdir" property.

...

zfs snapshot [-r] [-o property=value] ...
filesystem@snapname|volume@snapname

Creates a snapshot with the given name. See the
"Snapshots" section for details.

-r

Recursively create snapshots of all descendent
datasets. Snapshots are taken atomically, so that
all recursive snapshots correspond to the same
moment in time.

-o property=value

Sets the specified property; see "zfs create" for
details.