By default (mode=retain), Adaptive Server temporarily deactivates the specified device; you can reactivate it later. This is similar to what happens when a device fails and Adaptive Server activates its mirror:
I/O is directed only at the remaining device of the mirrored pair.
The status column of sysdevices is altered to indicate that the mirroring feature has been deactivated.
The entries for primary (phyname) and secondary (mirrorname) disks are unchanged.
