VERITAS Volume Manager 4.1 Administrator's Guide

Administering Hot-Relocation
How Hot-Relocation works
Chapter 9 327
How Hot-Relocation works
Hot-relocation allows a system to react automatically to I/O failures on
redundant (mirrored or RAID-5) VxVM objects, and to restore
redundancy and access to those objects. VxVM detects I/O failures on
objects and relocates the affected subdisks to disks designated as spare
disks or to free space within the disk group. VxVM then reconstructs the
objects that existed before the failure and makes them redundant and
accessible again.
When a partial disk failure occurs (that is, a failure affecting only some
subdisks on a disk), redundant data on the failed portion of the disk is
relocated. Existing volumes on the unaffected portions of the disk remain
accessible.
NOTE Hot-relocation is only performed for redundant (mirrored or RAID-5)
subdisks on a failed disk. Non-redundant subdisks on a failed disk are
not relocated, but the system administrator is notified of their failure.
Hot-relocation is enabled by default and takes effect without the
intervention of the system administrator when a failure occurs.
The hot-relocation daemon, vxrelocd, detects and reacts to VxVM
events that signify the following types of failures:
• disk failure—this is normally detected as a result of an I/O failure
from a VxVM object. VxVM attempts to correct the error. If the error
cannot be corrected, VxVM tries to access configuration information
in the private region of the disk. If it cannot access the private
region, it considers the disk failed.
• plex failure—this is normally detected as a result of an uncorrectable
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 vxrelocd detects such a failure, it performs the following steps: