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9.1 Snapshot – Fast Point-In-Time copies
Snapshots are read-only copies of file-systems at a specific point in time. Snapshot distinguishes
itself in its speed. Creating a snapshot is not involved with copying user data, thus usually taking
less than a second.
The concept of snapshot is very different from backups. Data are not copied to any media during
backup. Instead, it just informs the NAS that all the data blocks in use should be preserved, not
being overwritten. That is why it can be so fast. The "copy" occurs during everyday file access.
When a file is modified after a snapshot is created, its original data blocks are protected from being
overwritten. The new updates are written to a new location. The file-system maintains records and
pointers to keep track of the snapshot data and file changes.
Snapshot management
To manage snapshots, please open the administration page.
Enter the Backup→Snapshot→Manage page and select a volume.
Viewing Snapshot Information
On the page shows the snapshots existing on the volume and their information. Snapshot Used
Space indicates the disk space used by snapshot data. In the table – List of Snapshots, Space
to Free indicates the disk space which will be freed if a snapshot is deleted. Activity indicates
whether the snapshot is being deleted or rolled back.
Configuring snapshot settings
Item
With the .snap folders enabled, end-users can access snapshot data
without intervention of MIS people, retrieving previous versions of files
Show the .snap
from the .snap folders.
folder
Administrators can choose to show the .snap folders under the root of a
volume, or under all folders.
Using the AFP protocol, the folders with names beginning with dot (.) will
be hidden and not able to be accessed by Macintosh clients. To make
Name the .snap
the .snap folders visible, the administrators can choose to show
folder as ~snap
the .snap folders as ~snap instead so that the folders can be accessed
by Macintosh clients.
Delete
If enabled, it will automatically delete the oldest snapshots to free more
snapshots if free
disk space when the free space is lower than the specified percentage.
space is low
They specify how many hourly, daily, weekly and monthly snapshots to
keep, respectively. If the limit is exceeded, the oldest snapshot of the
Snapshot Policy
same type will be deleted. If not specified, it will keep the snapshots until
being manually deleted.
Creating snapshots
There are several ways to create snapshots. One is to create a snapshot manually by selecting a
volume and clicking the Create Snapshot button on the Snapshot→Manage page. It will create a
snapshot with a name like manual-20041010.190000, which indicates a snapshot created
manually at 19:00 on October 10, 2004. Another method is to set schedules to create snapshots
regularly. Moreover, the NAS server will create snapshots automatically when doing backup,
SmartSync and CD/DVD-burning tasks. Then it reads in source data from the automatically
4-Bay SATA NAS RAID Server with iSCSI
Chapter 9. Backup and Recovery
Description
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NAS-7410
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