Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

Creating consistency group Snapshot Virtual Disk

A consistency group snapshot virtual disk comprises multiple snapshot virtual disks to provide host access to a snapshot image that has been taken for each selected member virtual disk at the same moment in time. 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 that you select in the wizard 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 at the same time the consistency group snapshot virtual disk is created.

1. From the AMW, select the Storage & Copy Services tab.
2. Do one of the following:
   • Select a consistency group, and then select Copy Services > Consistency Group > Create Consistency Group Snapshot Virtual Disk. The Select Existing Snapshot Image or New Snapshot Image window is displayed. Go to step 3.
   • Select a consistency group snapshot image from the Consistency Group Snapshot Images table, and then select Copy Services > Consistency Group Snapshot Image > Create Consistency Group Snapshot Virtual Disk. The Consistency Group Snapshot Virtual Disk Settings window is displayed. Go to step 4.
3. If you selected a consistency group in step 2, select the consistency group snapshot image for which you want to create a snapshot virtual disk. Do one of the following:
   • Select An existing snapshot image and then select a snapshot image from the consistency group snapshot images table and click Next.
   • Select A new snapshot image and then a snapshot group from the existing snapshot group table and then click Next.
   The Consistency Group Snapshot Virtual Disk Settings window is displayed.
4. In the Consistency group snapshot virtual disk name field, enter a unique name (30 character maximum) that best describes the consistency group selected for this snapshot image. For example, AccountingData.
   By default, the consistency group snapshot virtual disk name is shown in the name text box as:[consistency-group-name] - SV + sequence-number where SV (snapshot virtual disk) is the appended suffix and sequence-number is the chronological number of the snapshot virtual disk relative to the consistency group.

   For example, if you create the first snapshot virtual disk for a consistency group called “Accounting”, then the default name of the snapshot virtual disk is “Accounting_SV_01”. The default name of the next snapshot virtual disk you create based on “Accounting” is “Accounting_SV_02”.

   There is a 30-character limit. After you reach this limit, you can no longer type in the text box. If the consistency group name is 30 characters, then the default name for the group uses the base virtual disk name truncated enough to add the suffix “SV” and the sequence string.

5. In the Map to host drop-down, specify how you want to map the host for each snapshot virtual disk created for a selected member virtual disk.
   This map attribute is applied to every member virtual disk you select in the consistency group.

   The following guidelines apply:

   • Each host has its own logical unit number (LUN) address space and let the same LUN be used by different host groups or hosts to access snapshot virtual disks in a storage array.
   • You can define one mapping for each snapshot virtual disk in the storage array.
   • Mappings are shared between RAID controller modules in the storage array.
   • The same LUN cannot be used twice by a host group or a host to access a snapshot virtual disk. You must use a unique LUN.
   • An access virtual disk mapping is not required for out-of-band storage arrays.
6. Select how to grant host access to each selected member virtual disk’s snapshot virtual disk. Do one of the following:
   • Select Read/Write to provide the host application with WRITE access to a copy of the data contained in the snapshot image. A Read-Write snapshot virtual disk requires an associated repository.
   • Select Read Only to provide a host application with READ access to a copy of the data contained in the snapshot image, but without the ability to modify the snapshot image. A Read-Only snapshot virtual disk does not have an associated repository.
7. Select each member virtual disk in the consistency group for which you want to create a snapshot virtual disk.
   You can click Select all to create a snapshot virtual disk for each member virtual disk displayed in the select members table.
8. If you selected Read-Only host access in step 6, you can skip this step and go to step 9.
   NOTE: Repositories are not required for Read-Only snapshot virtual disks.
9. Select how you want to create the snapshot virtual disk repositories for each member in the consistency group. Do one of the following:
   • Select Automatic and click Finish to create each snapshot virtual disk repository with the default capacity settings. This option is the recommended one.
   • Select Manual and click Next to define the properties for each snapshot virtual disk repository; then click Finish to continue with the snapshot virtual disk creation process. You can click Edit individual repository candidates to manually edit a repository candidate for each member virtual disk.
   Use this option if you want to specify all the customizable settings for the snapshot virtual disk repository. The Manual method is considered advanced and only those who understand physical disk consistency and optimal physical disk configurations should use this method.
   The snapshot virtual disk and its properties for the associated consistency group are displayed in the navigation tree.