A consistency group is simultaneous snapshots of multiple virtual disks, thus ensuring consistent copies of a group of 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.
• If the base virtual disk resides on a standard disk group, the repository members for any associated consistency group, can reside on either a standard disk group or a disk pool. If a base virtual disk resides on a disk pool, all repository members for any associated consistency group must reside on the same disk pool as the base virtual disk.
• You cannot create a consistency group on a failed virtual disk.
• A consistency group contains one snapshot group for each virtual disk that is a member of the consistency group. You cannot individually manage a snapshot group that is associated with a consistency group. Instead you must perform the manage operations (create snapshot image, delete snapshot image or snapshot group, and rollback snapshot image) at the consistency group level. • If you attempt to create a consistency group snapshot image, the operation might remain in a
Pending state because of the following conditions:
– The base virtual disk that contains this consistency group snapshot image is a member of an asynchronous remote replication group.
– The base virtual disk is currently in a synchronizing operation. The consistency group snapshot image creation completes as soon as the synchronization operation is complete.
To create a consistency group:
1. From the AMW, select the Storage & Copy Services tab.
2. Select Copy Services → Consistency Group → Create.
The Consistency Group Settings window is displayed.
3. In the Consistency group name field, enter a unique name (30-character maximum) that best
describes the member virtual disks that you want to add for this group. By default, the consistency group name is shown in the name text box as:
CG + sequence-number
In this example, CG (Consistency Group) is the prefix and sequence-number is the chronological number of the consistency group, and is incremented based on how many consistency groups currently exist.
4. Select if you want to add the member virtual disks to the consistency group now or later:
• Select Add members now and then from the eligible member virtual disks, select the virtual disks that you want to add as members to the consistency group. If you choose this method, you must create a repository for each member of the consistency group. Go to step 5. You can click the
Select all check box to add all the virtual disks displayed in the Eligible virtual disks table to the consistency group.
• Select Add members later and then click Finish to create the consistency group without member
virtual disks. Go to step 6.
The Eligible virtual disks table shows only those virtual disks that are capable of being used in the consistency group. To be eligible to be a member of a consistency group, a virtual disk cannot be in a Failed state and must contain less than the maximum allowable number of associated snapshot groups.
5. Select how you want to create the repositories for each member in the consistency group.
• Select Automatic and click Finish to create the repositories with the default capacity settings. This option is the recommended one.
• Select Manual and click Next to define the capacity settings for the repositories; and then click
Finish to continue with the consistency group creation process. You can click Edit individual repository candidates to manually edit a repository candidate for each member virtual disk.
NOTE: Use this option if you want to specify all of the customizable settings for the repositories. The Manual method is considered advanced and only those who understand physical disk consistency and optimal physical disk configurations should use this method.
6. Click Finish.
In the navigation tree, the consistency group and its properties are displayed under the Consistency
Groups node.
Creating A Consistency Group Repository (Manually)
During the creation of a consistency group, a consistency group repository is created to store the data for all the snapshot images contained in the group. A consistency group's repository is created initially with one individual repository virtual disk.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 every member virtual disk in the consistency group to save the data for all the snapshot images contained in the group.
The Manual method is considered advanced and only those who understand physical disk consistency, provisioning, and optimal physical disk configurations should use this method.
Keep these guidelines in mind when you name a consistency group:
• There is a minimum required capacity for a consistency group repository (depending on your configuration).
• When you define the capacity requirements for a repository, keep in mind any future requirements that you might have for other virtual disks in this disk group or disk pool. Make sure that you have enough capacity to meet your data storage needs, but you do not over allocate because you can quickly use up all the storage in your storage array.
• The list of repository candidates can contain both new and existing repository virtual disks. Existing repository virtual disks are left on the storage array by default when you delete a consistency group. Existing repository virtual disks are placed at the top of the list. The benefit to reusing an existing repository virtual disk is that you can avoid the initialization process that occurs when you create a new one.
To create a consistency group repository:
1. From the AMW, select the Storage & Copy Services tab.
2. Select Copy Services→ Consistency Group→ Create.
The Consistency Group Settings window is displayed.
3. Select Manual and click Next to customize the repository candidate settings for the consistency
group.
The Consistency Group Repository Settings - Manual window is displayed.
4. Select how you want to filter the repository candidates for each member virtual disk in the
consistency group, based on either a percentage of the base virtual disk capacity or by preferred capacity.
The best repository candidate for each member virtual disk based on the selections you made is displayed.
5. Select Edit individual repository candidates if you want to edit repository candidates for the
member virtual disks.
6. Select the repository, from the Repository candidates table, that you want to use for each member
virtual disk in the consistency group.
NOTE: Select a repository candidate that is closest to the capacity you specified.
• The Repository candidates table shows both new and existing repositories that are capable of
being used for each member virtual disk in the consistency group based on the value you specified for percentage or the value you specified for preferred capacity.
repository candidates, and those with different Data Service (DS) attributes. If appropriate
candidates are not returned using these settings, you can click Run Auto-Choose to provide
automatic candidate recommendations.
• The Difference column shows the mathematical difference between your selected capacity and
the actual capacity of the repository candidate. If the repository candidate is new, the system uses the exact capacity size that you specified and displays zero (0) in the Difference column.
7. To edit an individual repository candidate:
a. Select the candidate from the Repository candidates table and click Edit to modify the capacity
settings for the repository. b. Click OK.
8. Select View advanced options and then accept or change the following default settings as
appropriate.
9. Click Finish.