Snapshots 9-1

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A snapshot is a read-only copy of the entire file systemit reflects the state of the file
system at the time the snapshot was created.
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Any client of a filer can access snapshots to recover old versions of files; for example,
files that were accidentally changed or deleted. The snapshot feature enables users to
restore their own files without help, because files in snapshots can be viewed and
copied by those who have permission to do so with the original files.
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Snapshots also simplify tape backup. The filer dump command automatically creates a
snapshot of the active file system, if necessary, before backing up the data to tape.
However, it is not necessary if you are backing up an existing snapshot. Because a
snapshot is a read-only copy of the file system, it does not change even when files in
the active file system are changing. As a result, dump can make a safe and consistent
backup without requiring you to take the filer off-line.
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The filer uses a copy-on-write technique to create snapshots quickly without consum-
ing any disk space. Snapshots begin to consume extra space only as blocks in the
active file system are modified and written to new locations on disk. For more infor-
mation about the copy-on-write technique used by snapshots, refer to How
Snapshots Work.
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The filer creates and deletes snapshots automatically at preset intervals. You can also
create and delete snapshots manually. Each volume on the filer can have up to 20 dif-
ferent snapshots at one time.