A mirror can be added to an existing volume with the vxassist command, as follows:
# vxassist [-b] [-g diskgroup] mirror volume
If specified, the -b option makes synchronizing the new mirror a background task.
For example, to create a mirror of the volume voltest in the disk group, mydg, use the following command:
# vxassist -b -g mydg mirror voltest
Another way to mirror an existing volume is by first creating a plex, and then attaching it to a volume, using the following commands:
# vxmake [-g diskgroup] plex plex sd=subdisk ... # vxplex [-g diskgroup] att volume plex