VERITAS Volume Manager 3.5 User's Guide - VERITAS Enterprise Administrator (June 2002)

Commands for Hot Relocation
62 VERITAS Volume Manager User’s Guide - VEA
Commands for Hot Relocation
The Hot Spare and Hot Relocation procedures enable a system to automatically react to
I/O failures on redundant (mirrored or RAID-5) volumes, and to restore redundancy and
access to those volumes. The following commands can be used to perform relocation
tasks:
◆ Undoing Hot Relocation
◆ Clearing Relocation Information for Dynamic Disk Groups
◆ Customizing Disks for Hot Relocation
Note The Hot Relocation and Hot Spare operations are only performed for redundant
(mirrored or RAID-5)subdisks on a faileddisk. Non-redundantsubdisks ona failed
disk are not relocated, but the system administrator is notified of their failure.
About Hot Spare and Hot Relocation
One or more disks in each dynamic disk group can be designated as hot spares by using
the“set diskusage”command. These hot sparedisks providealocation wheredata can be
moved from failed disks or volumes.
In Hot Spare mode, all subdisks containing redundant volumes will be moved together
froma failed disk to a spare disk. In orderfor the Hot Spareoperation to occur, theremust
be enough free space on the spare disk for all the redundant volumes from the original
disk.
When a disk fails, hot relocation automatically moves all subdisks containing redundant
volumes from thefailed disk tohot spare disks. If nodisks havebeen designatedas spares
or there is not enough spare disk space, a combination of spare space and free space is
used. Depending on available disk space, the subdisks are not always all moved to the
same disk, but may be scattered within the dynamic disk group.
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 and the existing
volumes comprised of the unaffected portions of the disk remain accessible.
When selecting space for relocation, hot relocation preserves the redundancy
characteristics of the Volume Manager object that the relocated subdisk belongs to. For
example, hotrelocation ensures thatsubdisks from afailed plex are notrelocated to adisk
containing a mirror of the failed plex. If redundancy cannot be preserved using any
available spare disks 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.