VERITAS Volume Manager 3.1 Administrator's Guide

Initialization and Setup
Protecting Your System
Chapter 2 81
Protecting Your System
Disk failures can cause two types of problems: loss of data on the failed
disk and loss of access to your system. Loss of access can be due to the
failure of a key disk (a disk used for system operations). The VERITAS
Volume Manager can protect your system from these problems.
To maintain system availability, data important to running and booting
your system must be mirrored. The data must be preserved so it can be
used in case of failure.
Here are suggestions on how to protect your system and data:
• Use mirroring to protect data. By mirroring your data, you prevent
data loss from a disk failure. To preserve data, create and use
mirrored volumes that have at least two data plexes. The plexes must
be on different disks. If a disk failure causes a plex to fail, the data in
the mirrored volume still exists on the other disk.
If you use the vxassist mirror command to create mirrors, it locates
the mirrors so the loss of one disk does not result in a loss of data. By
default, the vxassist command does not create mirrored volumes;
edit the file /etc/default/vxassist to set the default layout to
mirrored. For information on the vxassist defaults file, see “vxassist
Command”.
• Leave the Volume Manager hot-relocation feature enabled to
automatically detect failures, notify you of the nature of the failures,
attempt to relocate any affected subdisks that are redundant, and
initiate recovery procedures. Provide at least one hot-relocation spare
disk per disk group so sufficient space is available for relocation in
the event of a failure.
• For mirrored volumes, take advantage of the Dirty Region Logging
feature to speed up recovery of your mirrored volumes after a system
crash. Make sure that each mirrored volume has at least one log
subdisk. (Note that the usr volume cannot have Dirty Region
Logging turned on.)
• For RAID-5 volumes, take advantage of logging to prevent corruption
of recovery data. Make sure that each RAID-5 volume has at least one
log plex.
• Perform regular backups to protect your data. Backups are necessary