Understanding Snapshot copies

What a Snapshot copy is

A Snapshot copy is a frozen, read-only image of a traditional volume, a FlexVol volume, or an aggregate that reflects the state of the file system at the time the Snapshot copy was created. Snapshot copies are your first line of defense for backing up and restoring data. See the Storage Management Guide for information about traditional volumes, FlexVol volumes, or aggregates.

When Snapshot copies are created

Data ONTAP maintains a configurableSnapshot schedule that creates and deletes Snapshot copies automatically for each volume. See Creating Snapshot schedules. Snapshot copies can also be created and deleted manually.

Maximum number of Snapshot copies

You can store up to 255 Snapshot copies at one time on each volume.

Maximum space Snapshot copies can occupy

You can specify the percentage of disk space that Snapshot copies can occupy. The default setting is 20% of the total (both used and unused) space on the disk. For a full explanation of how Snapshot copies consume disk space, see Understanding Snapshot disk consumption.

How Snapshot copies handle file permissions

Snapshot files carry the same permissions and inode numbers as the original files, keeping the integrity of the security system intact. Inodes are data structures that hold information (including permissions information) about files on the storage system. There is an inode for each file and a file is uniquely identified by the file system on which it resides and its inode number on that system.

Note
The inode number for a file in a Snapshot copy is the same as the inode number for the corresponding file in the active file system. As a result, some programs on UNIX clients consider the two files to be the same. For example, if you use the GNU diff program to compare the two files, it does not find any differences between them. In some cases, if you try to restore a file from a Snapshot copy, you might see the following error message:

cp:.snapshot/xxx and xxx are identical.

To make sure that the two files have different inode numbers before the copy or comparison, copy one of the files to different name.

What you can do with Snapshot copies

Snapshot copies enable system administrators to

Create instantaneous backups
Create a clone of a FlexVol volume
Create a clone of a Data ONTAP LUN
Note
See the Storage Management Guide for information about cloning a FlexVol volume. See your Block Access Management Guide for information about cloning a Data ONTAP LUN.

Snapshot copies enable end-users to

Recover older versions or sets of files that were accidentally changed or deleted
Restore their own files without needing a system administrator to restore files from tape