By default, the vxassist command allocates space from any disk that has free space. You can reserve a set of disks for special purposes, such as to avoid general use of a particularly slow or a particularly fast disk.
To reserve a disk
# vxedit [-g diskgroup] set reserve=on diskname
After you enter this command, the vxassist program does not allocate space from the selected disk unless that disk is specifically mentioned on the vxassist command line. For example, if mydg03 is reserved, use the following command:
# vxassist [-g diskgroup] make vol03 20m mydg03
# vxassist -g mydg make vol04 20m