When you create a , you create a that has a and a on the same storage array.
Attention:
Possible loss of data access – This option overwrites existing data on the target virtual disk and renders the target virtual disk read-only to hosts. This option fails all of the snapshot virtual disks that are associated with the target virtual disk, if any exist.The target virtual disk is a virtual disk to which you want to copy the data from the source virtual disk. The target virtual disk can be a standard virtual disk or the source virtual disk of a snapshot virtual disk that has stopped or failed.
After the virtual disk copy has completed, the target virtual disk automatically becomes read-only to hosts. Additionally, write requests to the target virtual disk are rejected. After the virtual disk copy has completed, you can change the Read-Only attribute. To change the Read-Only attribute, click the Modify tab, and click the Manage Virtual Disk Copies link.