Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

371Administering hot-relocation
How hot-relocation works
■ If no spare disks are available or additional space is needed, vxrelocd uses free
space on disks in the same disk group, except those disks that have been excluded for
hot-relocation use (marked nohotuse). When vxrelocd has relocated the
subdisks, it reattaches each relocated subdisk to its plex.
■ Finally, vxrelocd initiates appropriate recovery procedures. For example, recovery
includes mirror resynchronization for mirrored volumes or data recovery for RAID-5
volumes. It also notifies the system administrator of the hot-relocation and recovery
actions that have been taken.
If relocation is not possible,
vxrelocd notifies the system administrator and takes no
further action.
Note: Hot-relocation does not guarantee the same layout of data or the same performance
after relocation. The system administrator can make configuration changes after
hot-relocation occurs.
Relocation of failing subdisks is not possible in the following cases:
■ The failing subdisks are on non-redundant volumes (that is, volumes of types other
than mirrored or RAID-5).
■ There are insufficient spare disks or free disk space in the disk group.
■ The only available space is on a disk that already contains a mirror of the failing plex.
■ The only available space is on a disk that already contains the RAID-5 log plex or
one of its healthy subdisks. Failing subdisks in the RAID-5 plex cannot be relocated.
■ If a mirrored volume has a dirty region logging (DRL) log subdisk as part of its data
plex, failing subdisks belonging to that plex cannot be relocated.
■ If a RAID-5 volume log plex or a mirrored volume DRL log plex fails, a new log
plex is created elsewhere. There is no need to relocate the failed subdisks of the log
plex.
See the
vxrelocd(1M) manual page for more information about the hot-relocation
daemon.
Figure 12-1 illustrates the hot-relocation process in the case of the failure of a single
subdisk of a RAID-5 volume.