VERITAS Volume Manager 3.1 Administrator's Guide

Recovery
Detecting and Replacing Failed Disks
Chapter 8348
I/O error in the plex (which affects subdisks within the plex). For
mirrored volumes, the plex is detached.
• RAID-5 subdisk failure—this is normally detected as a result of an
uncorrectable I/O error. The subdisk is detached.
When such a failure is detected, the vxrelocd daemon informs the
system administrator by electronic mail of the failure and which Volume
Manager objects are affected. The vxrelocd daemon then determines
which subdisks (if any) can be relocated. If relocation is possible, the
vxrelocd daemon finds suitable relocation space and relocates the
subdisks.
Hot-relocation space is chosen from the disks reserved for hot-relocation
in the disk group where the failure occurred. If no spare disks are
available or additional space is needed, free space in the same disk group
is used. Once the subdisks are relocated, each relocated subdisk is
reattached to its plex.
Finally, the vxrelocd daemon initiates appropriate recovery procedures.
For example, recovery includes mirror resynchronization for mirrored
volumes or data recovery for RAID-5 volumes. The system administrator
is notified of the hot-relocation and recovery actions taken.
If relocation is not possible, the system administrator is notified and no
further action is taken. Relocation is not possible in the following cases:
• If subdisks are not redundant (that is, they do not belong to mirrored
or RAID-5 volumes), they cannot be relocated.
• If enough space is not available (from spare disks and free space) in
the disk group, failing subdisks cannot be relocated.
• If the only available space is on a disk that already contains a mirror
of the failing plex, the subdisks in that plex cannot be relocated.
• If the only available space is on a disk that already contains the
RAID-5 plex log plex or one of its healthy subdisks, the failing
subdisk in the RAID-5 plex cannot be relocated.
• If a mirrored volume has a Dirty Region Logging log subdisk as part
of its data plex, 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 (so the log plex is not actually
relocated).
You can prepare for hot-relocation by designating one or more disks per