Administrator Guide

Consistency group repositories
A consistency group is made up of simultaneous snapshots of multiple virtual disks. Each virtual disk that belongs to a consistency group is
referred to as a member virtual disk. When you add a virtual disk to a consistency group, the system automatically creates a new snapshot
group that corresponds to this member virtual disk. A consistency group repository must be created for each member virtual disk in a
consistency group in order to save data for all snapshot images in the group.
A consistency group snapshot image comprises multiple snapshot virtual disks. Its purpose is to provide host access to a snapshot image
that has been taken for each member virtual disk at the same moment in time. A consistency group snapshot image is not directly read or
write accessible to hosts; it is used only to save the data captured from the base virtual disk. The consistency group snapshot virtual disk
can be designated as either read-only or read-write. Read-write consistency group snapshot virtual disks require a repository for each
member virtual disk in order to save any subsequent modifications made by the host application to the base virtual disk without affecting
the referenced snapshot image. Each member repository is created when the consistency group snapshot virtual disk is created.
Ranking repository candidates
If you choose to create a repository manually, you can filter repository candidates for each member virtual disk by selecting either a
percentage of the base virtual disk capacity or by specifying a preferred capacity in the Snapshot Group Settings window. Based on
your selection, best repository candidates are displayed. Repository candidates shown contain both new and existing repository virtual
disks residing on a disk group or disk pool.
Using snapshot consistency group to a Remote Replication
Although a virtual disk can belong to multiple consistency groups, you must create separate consistency groups for snapshot images and
Remote Replication.
Adding a base virtual disk containing a consistency group to a Remote Replication (non-legacy, asynchronous), the repository
automatically purges the oldest snapshot image and sets the auto-delete limit to the maximum allowable snapshot limit for a consistency
group.
Additionally, all member virtual disks belonging to both a snapshot consistency group and a Remote Replication group must belong to the
same Remote Replication group.
Creating snapshot images
A snapshot image is a logical point-in-time image of the content of an associated base virtual disk. With snapshot images, you can create
multiple copies of production data on your storage array much more quickly than full copies. Snapshot images track source changes from
the time each snapshot image is created. You can create snapshot images for the following storage objects:
• Standard virtual disks
• Thin virtual disks
• Consistency groups
Before creating a snapshot image, consider these guidelines:
• If you attempt to create a snapshot image on a snapshot group and that snapshot group has reached its maximum number of
snapshot images, you can retry creating snapshot images after doing one of the following:
○ Enable automatic deletion of snapshot images in the Advanced Options section of the Create wizard.
○ Manually delete one or more snapshot images from the snapshot group.
• If you attempt to create a snapshot image and either of the following conditions below are present, the creation may remain in
Pending state:
○ The base virtual disk that contains this snapshot image is a member of an Remote Replication group.
○ The base virtual disk is currently synchronizing. When synchronization is complete, the snapshot image creation will complete.
• You cannot create a snapshot image on a failed virtual disk or on a snapshot group designated as Reserved.
Creating snapshot image
You can create a snapshot image by either selecting a base virtual disk or by selecting an existing snapshot group.
To create a snapshot image from an existing base virtual disk:
1. From the AMW, select the base virtual disk you are copying and select Copy Services > Snapshot Image > Create.
Premium feature—Snapshot Virtual Disk
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