HP StorageWorks 8000, Руководство пользователя

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Managing Your Storage
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Replicating Data with Snapshots
Using Snapshots
WARNING: When using an EVA array in a SAN environment, do not use the
SAN appliance HSV Element Manager to create hardware snapshots, because
the the NAS 8000 will not recognize them. Instead, you should use Command
View NAS to make snapshots of data. For more detailed information about
SAN array limitations, see the HP support web site at
http://hp.com/support/nas8000 for a technical paper called
HP StorageWorks
NAS 8000 SAN Storage Configuration Guide
.
A snapshot is a read-only picture of a file volume at a specific point in time. When
you create a file volume, the snapshot of that file volume is of zero size. However,
as you modify the file volume, the snapshot tracks changes between the original
file volume and the modified file volume. If an error occurs and you want to revert
to the previous version, you can use the snapshot data and the unmodified parts of
the original file volume to quickly and easily construct the file volume.
When you set up a snapshot, consider how quickly the file’s data will change, and
how often you will delete snapshots and start over. You have the option to size
snapshots relatively small and let them autogrow. As they reach the limit that you
establish, their size can increase by approximately 10 percent to accommodate the
changes. This flexibility lets you set the snapshot and not worry about a specific
size.
The default snapshot size is 10 percent of the size of the file volume being
snapped. The required snapshot size is dependent on the data’s rate of change, and
this value may not be applicable for all environments. Enabling the autogrow
feature helps prevent filling a snapshot and rendering it useless.
After you specify a size, you must define an expiration date. When the snapshot
expires, the system automatically deletes it. Consider your overall backup strategy
in light of the snapshot expiration date. For example, you may want to take a
snapshot of your data for a specified amount of time, then when you are certain
that you have a backup of your system, delete the snapshot and begin the snapshot
process again.