Adding a mirrored copy to a VDisk

Use the Add Copy to VDisk panel in the SAN Volume Controller Console to add a mirrored copy to the selected virtual disk (VDisk). Each VDisk can have a maximum of two copies.

Creating mirrored copies of a VDisk allows the VDisk to remain accessible even when a managed disk (MDisk) that the VDisk depends on becomes unavailable. You can create copies of a VDisk either from different MDisk groups or by creating an image mode copy of the VDisk. Copies allow for availability of data; however, they are not separate objects. You can only create or change mirrored copies from the VDisk.

In addition, you can use VDisk mirroring as an alternative method of migrating VDisks between MDisk groups. For example, if you have a nonmirrored VDisk in one MDisk group and want to migrate that VDisk to a second MDisk group, you can add a new copy of the VDisk by specifying the second MDisk group for that VDisk copy. After the copies have synchronized, you can delete the copy in the first MDisk group. The VDisk is migrated to the second MDisk group while remaining online during the migration.

This alternative method of migrating VDisks has the following advantages:

Access to the VDisk data is not lost if the second MDisk group goes offline during the migration.
The speed of the migration can be adjusted, using the VDisk synchronization rate, and the migration can be paused.
The migration can be ended by deleting the VDisk copy in the second MDisk group before migration completes.
The MDisk groups can have different extent sizes.

This alternative method of migrating VDisks has the following limitations:

You cannot use this method for VDisks that are already mirrored.
There are more manual steps that are associated with this method.
Write I/O performance is slightly affected during the migration, because the mirrored copies must be kept synchronized.

This task assumes that you have already launched the SAN Volume Controller Console.

Perform the following steps to add a mirrored copy to a VDisk:

Click Work with Virtual Disks > Virtual Disks in the portfolio. The Viewing Virtual Disks panel is displayed.
Select the VDisk to copy and select Add Mirrored VDisk Copy from the task list. Click Go. The Add Copy to VDisk panel is displayed.
Select the type of VDisk copy and then select the managed disk (MDisk) group to create the VDisk copy from. View the panel Help for more information about the options that are available on this panel.
Click OK to add a mirrored copy to the selected VDisk.