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

• Back up data.
• Copy data from disk groups that use smaller-capacity physical disks to disk groups using greater capacity physical disks.
• Restore snapshot virtual disk data to the source virtual disk.

Virtual disk copy generates a full copy of data from the source virtual disk to the target virtual disk in a storage array.

• Source virtual disk—When you create a virtual disk copy, a copy pair consisting of a source virtual disk and a target virtual disk is created on the same storage array. When a virtual disk copy is started, data from the source virtual disk is copied completely to the target virtual disk.
• Target virtual disk—When you start a virtual disk copy, the target virtual disk maintains a copy of the data from the source virtual disk. You can choose whether to use an existing virtual disk or create a new virtual disk as the target virtual disk. If you choose an existing virtual disk as the target, all data on the target is overwritten. A target virtual disk can be a standard virtual disk or the source virtual disk of a failed or disabled snapshot virtual disk.
  NOTE: The target virtual disk capacity must be equal to or greater than the source virtual disk capacity.
  When you begin the disk copy process, you must define the rate at which the copy is completed. Giving the copy process top priority slightly impacts I/O performance, while giving it lowest priority makes the copy process longer to complete. You can modify the copy priority while the disk copy is in progress.