Administrator Guide

Premium feature—Snapshot Virtual Disk

The following virtual disk snapshot premium feature is supported on the MD storage array:

• Snapshot Virtual Disks using multiple point-in-time (PiT) groups

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 because 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.

Topics:

• Snapshot images and groups

• Snapshot Virtual Disk read/write properties

• Snapshot groups and consistency groups

• Understanding snapshot repositories

• Creating snapshot images

• Scheduling snapshot images

• Performing snapshot rollbacks

• Creating snapshot group

• Converting a snapshot Virtual Disk to read-write

• Viewing associated physical components of an individual repository virtual disk

• Creating consistency group

• Creating a snapshot virtual disk of a snapshot image

• Creating consistency group Snapshot Virtual Disk

Snapshot images and groups

Snapshot images can be created manually or automatically by establishing a schedule that defines the date and time you want the

snapshot image created. The following objects can be included in a snapshot image:

• Standard virtual disks

• Thin provisioned virtual disks

• Consistency groups

To create a snapshot image, you must first create a snapshot group and reserve snapshot repository space for the virtual disk. The

repository space is based on a percentage of the current virtual disk reserve.

You can delete the oldest snapshot image in a snapshot group either manually or you can automate the process by enabling the Auto-

Delete setting for the snapshot group. When a snapshot image is deleted, its definition is removed from the system, and the space

occupied by the snapshot image in the repository is released and made available for reuse within the snapshot group.

Snapshot Virtual Disk read/write properties

A snapshot virtual disk can be designated as either read-only or read-write.

The following are the differences between the two:

• Read-Only snapshot virtual disks provide the host read access to a copy of the data contained in the snapshot image. However, the

host cannot modify the snapshot image. A Read-Only snapshot virtual disk does require an associated repository.

• Read-Write snapshot virtual disks require an associated repository to provide the host write access to a copy of the data contained in

the snapshot image. A Read-Write snapshot virtual disk requires its own repository to save any subsequent modifications made by the

host application to the base virtual disk without affecting the referenced snapshot image. The snapshot is allocated from the storage

pool from which the original snapshot image is allocated. All I/O writes to the snapshot image are redirected to the snapshot virtual

disk repository that was allocated for saving data modifications. The data of the original snapshot image remains unchanged. For more

information, see Understanding Snapshot Repositories.

Premium feature—Snapshot Virtual Disk 99