The act of promoting the to be the of the mirrored virtual disk pair, and demoting the primary virtual disk to be the secondary virtual disk.
You can perform a role reversal either by:
Selecting a secondary virtual disk and selecting Virtual Disk >> Remote Virtual Disk Mirroring >> Change >> Role to Primary.
-or-
Selecting a primary virtual disk and selecting Virtual Disk >> Remote Virtual Disk Mirroring >> Change >> Role to Secondary.
Both options result in the promotion of the secondary virtual disk and the demotion of the primary virtual disk to effect the role reversal.
If communication with the remote is down, you can force a role reversal even when there will be a resulting or condition. Use the Recovery Guru to recover from one of those conditions after communication is restored with the remote storage array.
You can also perform a role reversal using the set command in the Script Editor or on the command line. See "Using the set Command" in the online help.