Tandberg Data NAS Hardware Viking FS-1500 - Manual (Page 39)

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4-1 Tandberg Viking Series Storage Server Administration Manual
4.
Volume Shadow Copy
Service(VSS)
4.1. Volume Shadow Copy Service Overview
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 under Windows® Storage Server 2003
environment.
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 Viking Series NAS appliance (see the “Managing Shadow
Copy” section in this chapter), 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 works at the block level. As changes are made to
the file system, the Shadow Copy Service copies out the original blocks to a
special cache file, to maintain a consistent view of the file at a particular
point in time. Since 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 since blocks are not moved
until an update to the disk occurs.
By using shadow copies, the NAS appliance 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. Since a
snapshot only contains a portion of the original data blocks, shadow copies
can not 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.