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

If you require RAID-5 logs, you must use the logdisk attribute to specify the disks
to be used for the log plexes.
RAID-5 logs can be concatenated or striped plexes, and each RAID-5 log associated
with 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 volumelength \
layout=raid5 [ncol=number_columns] [nlog=number] \
[loglen=log_length] logdisk=disk[,disk,...] \
storage_attributes
For example, the following command creates a 3-column RAID-5 volume with the
default stripe unit size on disks mydg04, mydg05 and mydg06. It also creates two
RAID-5 logs on disks mydg07 and mydg08.
# vxassist -b -g mydg -o ordered make volraid 10g layout=raid5 \
ncol=3 nlog=2 logdisk=mydg07,mydg08 mydg04 mydg05 mydg06
The number of logs must equal the number of disks that is specified to logdisk.
See “Specifying ordered allocation of storage to volumes” on page 308.
See the vxassist(1M) manual page.
It is possible to add more logs to a RAID-5 volume at a later time.
See “Adding a RAID-5 log” on page 382.
Creating tagged volumes
Volume tags are used to implement the SmartTier feature of the Storage
Foundation software.
See the Veritas Storage Foundation Advanced Features Administrator’s Guide.
Creating volumes
Creating tagged volumes
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