A spare disk must be initialized and placed in a disk group as a spare before it can be used for replacement purposes. If no disks have been designated as spares when a failure occurs, VxVM automatically uses any available free space in the disk group in which the failure occurs. If there is not enough spare disk space, a combination of spare space and free space is used.
The free space used in hot-relocation must not have been excluded from hot-relocation use. Disks can be excluded from hot-relocation use by using vxdiskadm, vxedit or Storage Foundation Manager (SFM).
You can designate one or more disks as hot-relocation spares within each disk group. Disks can be designated as spares by using vxdiskadm, vxedit, or SFM. Disks designated as spares do not participate in the free space model and should not have storage space allocated on them.
When selecting space for relocation, hot-relocation preserves the redundancy characteristics of the VxVM object to which the relocated subdisk belongs. For example, hot-relocation ensures that subdisks from a failed plex are not relocated to a disk containing a mirror of the failed plex. If redundancy cannot be preserved using any available spare disks and/or free space, hot-relocation does not take place. If relocation is not possible, the system administrator is notified and no further action is taken.
From the eligible disks, hot-relocation attempts to use the disk that is "closest" to the failed disk. The value of "closeness" depends on the controller and disk number of the failed disk. A disk on the same controller as the failed disk is closer than a disk on a different controller.