Free space is used automatically by hot-relocation in case spare space is not sufficient to relocate failed subdisks. You can limit this free space usage by hot-relocation by specifying which free disks should not be touched by hot-relocation. If a disk was previously excluded from hot-relocation use, you can undo the exclusion and add the disk back to the hot-relocation pool.
# vxedit [-g diskgroup] set nohotuse=off diskname
To use vxdiskadm to make a disk available for hot-relocation use
Enter disk name [<disk>,list,q,?] mydg01
V-5-2-932 Making mydg01 in mydg available for hot-relocation use is complete.
Make another disk available for hot-relocation use? [y,n,q,?] (default: n)