Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

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.
The following are suggestions for protecting your system and data:
■ Perform regular backups to protect your data. Backups are necessary if all
copies of a volume are lost or corrupted. Power surges can damage several (or
all) disks on your system. Also, typing a command in error can remove critical
files or damage a file system directly. Performing regular backups ensures
that lost or corrupted data is available to be retrieved.
■ Place the disk containing the root file system (the root or boot disk) under
Veritas Volume Manager control. Mirror the root disk so that an alternate root
disk exists for booting purposes. By mirroring disks critical to booting, you
ensure that no single disk failure leaves your system unbootable and unusable.
See “Rootability” on page 117.
■ Use mirroring to protect data against loss from a disk failure.
See “Mirroring guidelines” on page 553.
■ Use the DRL feature to speed up recovery of mirrored volumes after a system
crash.
See “Dirty region logging guidelines” on page 554.
■ Use striping to improve the I/O performance of volumes.
See “Striping guidelines” on page 554.
■ Make sure enough disks are available for a combined striped and mirrored
configuration. At least two disks are required for the striped plex, and one or
more additional disks are needed for the mirror.
■ When combining striping and mirroring, never place subdisks from one plex
on the same physical disk as subdisks from the other plex.
■ Use logging to prevent corruption of recovery data in RAID-5 volumes. Make
sure that each RAID-5 volume has at least one log plex.
See “RAID-5 guidelines” on page 555.
■ Leave the Veritas Volume Manager hot-relocation feature enabled.
See “Hot-relocation guidelines” on page 556.
Mirroring guidelines
Refer to the following guidelines when using mirroring.
■ Do not place subdisks from different plexes of a mirrored volume on the same
physical disk. This action compromises the availability benefits of mirroring
553Configuring Veritas Volume Manager
Guidelines for configuring storage