VERITAS Volume Manager 3.1 Administrator's Guide

Recovery
RAID-5 Volume Layout
Chapter 8 365
stored. Any other plexes associated with the volume are used to log
information about data and parity being written to the volume. These
plexes are referred to as RAID-5 log plexes or RAID-5 logs.
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. It is suggested that you have 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.
To support concurrent access to the RAID-5 array, the log should be
several times the stripe size of the RAID-5 plex.
You can tell the difference between a RAID-5 log plex and a RAID-5 plex
of a RAID-5 volume by examining vxprint output. The STATE field for a
log plex is marked as LOG. See the following vxprint output for a
RAID-5 volume:
VNAMERVGKSTATESTATELENGTHUSETYPEPREFPLEXRDPOL
PL NAMEVOLUMEKSTATESTATELENGTHLAYOUTNCOL/WIDMODE
SDNAMEPLEXDISKDISKOFFSLENGTH[COL/]OFFDEVICEMODE
vr5volRAID-5ENABLEDDEGRADED20480RAID-
plr5vol-01r5volENABLEDACTIVE20480RAID3/16RW
sddisk00-00r5vol-01disk000102400/0c1t4d1ENA
sddisk01-00r5vol-01disk010102401/0c1t2d1ENA
sddisk02-00r5vol-01disk020102402/0c1t3d1ENA
plr5vol-l1r5volENABLEDLOG1024CONCAT-RW
sddisk03-01r5vol-l1disk00010240c1t3d0ENA
plr5vol-l2r5volENABLEDLOG1024CONCAT-RW
sddisk04-01r5vol-l2disk02010240c1t1d1ENA
The RAID-5 volume (r5vol) can be identified as a RAID-5 volume by its
read policy being RAID. It has one RAID-5 plex (r5vol-01), similar to
the one described earlier. It has two RAID-5 logs in the plexes r5vol-l1
and r5vol-l2. These are identified by the state fieldbeing LOG and they
are associated with a RAID-5 volume and have a layout that is not RAID.