HP ML110 - ProLiant G5 2TB Storage Server NAS, Руководство пользователя

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Volume shadow copies
NOTE:
Select storage servers can be deployed in a clustered as well as a non-clustered configuration. This chapter
discusses using shadow copies in a non-clustered environment.
The Volume Shadow Copy Service provides an infrastructure for creating point-in-time snapshots
(shadow copies) of volumes. Shadow Copy supports 64 shadow copies per volume.
A shadow copy contains previous versions of the files or folders contained on a volume at a specific
point in time. While the shadow copy mechanism is managed at the server, previous versions of files
and folders are only available over the network from clients, and are seen on a per folder or file level,
and not as an entire volume.
The shadow copy feature uses data blocks. As changes are made to the file system, the Shadow Copy
Service copies the original blocks to a special cache file to maintain a consistent view of the file at a
particular point in time. Because the snapshot only contains a subset of the original blocks, the cache
file is typically smaller than the original volume. In the snapshot's original form, it takes up no space
because blocks are not moved until an update to the disk occurs.
By using shadow copies, a storage server can maintain a set of previous versions of all files on the
selected volumes. End users access the file or folder by using a separate client add-on program, which
enables them to view the file in Windows Explorer. Accessing previous versions of files, or shadow
copies, enables users to:
• Recover files that were accidentally deleted. Previous versions can be opened and copied to a
safe location.
• Recover from accidentally overwriting a file. A previous version of that file can be accessed.
• Compare several versions of a file while working. Use previous versions to compare changes
between two versions of a file.
Shadow copies cannot replace the current backup, archive, or business recovery system, but they
can help to simplify restore procedures. Because a snapshot only contains a portion of the original
data blocks, shadow copies cannot protect against data loss due to media failures. However, the
strength of snapshots is the ability to instantly recover data from shadow copies, reducing the number
of times needed to restore data from tape.
Shadow copy planning
Before setup is initiated on the server and the client interface is made available to end users, consider
the following:
• From what volume will shadow copies be taken?
• How much disk space should be allocated for shadow copies?
• Will separate disks be used to store shadow copies?
• How frequently will shadow copies be made?
Identifying the volume
Shadow copies are taken for a complete volume, but not for a specific directory. Shadow copies
work best when the server stores user files, such as documents, spreadsheets, presentations, graphics,
or database files.
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