Dell PowerVault MD3420 - Manual (Page 55)

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Using The Snapshot Feature
The following types of virtual disk snapshot premium features are supported on the MD storage array:
• Snapshot Virtual Disks using multiple point-in-time (PiT) groups
• Snapshot Virtual Disks (Legacy) using a separate repository for each snapshot
NOTE: This section describes the Snapshot Virtual Disk using PiT groups. If you are using the
Snapshot Virtual Disk (Legacy) premium feature, see
Using The Snapshot (Legacy) Feature .
A snapshot image is a logical image of the content of an associated base virtual disk created at a specific
point-in-time, often known as a restore point. This type of image is not directly readable or writable to a
host since the snapshot image is used to save data from the base virtual disk only. To allow the host to
access a copy of the data in a snapshot image, you must create a snapshot virtual disk. This snapshot
virtual disk contains its own repository, which is used to save subsequent modifications made by the host
application to the base virtual disk without affecting the referenced snapshot image.
Before Using Snapshot CLI Commands
There are two types of virtual disk snapshot premium features supported on your storage array.
Depending on your RAID controller firmware version, you may be using the legacy version of the
Snapshot feature. For more information, see
Using The Snapshot (Legacy) Feature .
NOTE: Ensure that you know which type of snapshot premium feature you have activated on your
storage array.
For information on the differences between the two snapshot features, see the Administrator's Guide.
Snapshot Images And Groups
A snapshot image is a logical image of the content of an associated base virtual disk created at a specific
point-in-time, also called a restore point. This type of image is not directly readable or writable to a host
since the snapshot image is used to save data from the base virtual disk only. To allow the host to access
a copy of the data in a snapshot image, you must create a snapshot virtual disk. This snapshot virtual disk
contains its own repository, which is used to save subsequent modifications made by the host application
to the base virtual disk without affecting the referenced snapshot image.
A snapshot image differs from a snapshot (legacy) in the following ways:
• A snapshot image uses one repository for all snapshot images associated with a base virtual disk,
improving performance when there are updates to the base virtual disk.
• A snapshot image only exists within a snapshot group. To make the snapshot image read/write
accessible by hosts, you must create a snapshot virtual disk.
For more information on the Snapshot feature, see the Administrator's Guide.
Only the following can be included in a snapshot image:
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