VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 7, Creating Volumes
Creating a RAID-5 Volume
177
A RAID-5 volume contains a RAID-5 data plex that consists of three or more subdisks
located on three or more physical disks. Only one RAID-5 data plex can exist per volume.
A RAID-5 volume can also contain one or more RAID-5 log plexes, which are used to log
information about data and parity being written to the volume. For more information on
RAID-5 volumes, see “RAID-5 (Striping with Parity)” on page 25.
Caution Do not create a RAID-5 volume with more than 8 columns because the volume
will be unrecoverable in the event of the failure of more than one disk.
To create a RAID-5 volume, use the following command:
# vxassist [-b] [-g diskgroup] make volume length layout=raid5 \
[ncol=number_columns] [stripewidth=size] [nlog=number] \
[loglen=log_length]
Note Specify the -b option if you want to make the volume immediately available for
use. See “Initializing and Starting a Volume” on page 181 for details.
For example, to create the RAID-5 volume volraid together with 2 RAID-5 logs, use the
following command:
# vxassist -b make volraid 10g layout=raid5 nlog=2
This creates a RAID-5 volume with the default stripe unit size on the default number of
disks. It also creates two RAID-5 logs rather than the default of one log.
Note If you require RAID-5 logs, you must use thelogdisk attribute tospecify the disks
to be used for the log plexes.
RAID-5 logs canbe concatenatedor stripedplexes, andeach RAID-5log associatedwith a
RAID-5 volume has a complete copy of the logging information for the volume. To
support concurrent access to the RAID-5 array, the log should be several times the stripe
size of the RAID-5 plex.
It is suggested that you configure a minimum of two RAID-5 log plexes for each RAID-5
volume. These log plexes should be located on different disks. Having two RAID-5 log
plexes for each RAID-5 volume protects against the loss of logging information due to the
failure of a single disk.
If you use ordered allocation when creating a RAID-5 volume on specified storage, you
must use the logdisk attribute to specify on which disks the RAID-5 log plexes should
be created. Use the following form of the vxassist command to specify the disks from
which space for the logs is to be allocated:
# vxassist [-b] [-g diskgroup] -o ordered make volume length \
layout=raid5 [ncol=number_columns] [nlog=number] \
[loglen=log_length] logdisk=disk[,disk,...] storage_attributes