A RAID-5 volume requires space to be available on at least as many disks in the disk group as the number of columns in the volume. Additional disks may be required for any RAID-5 logs that are created.
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.
# vxassist [-b] [-g diskgroup] make volume length layout=raid5 \ [ncol=number_of_columns] [stripewidth=size] [nlog=number] \ [loglen=log_length]
# vxassist -b -g mydg make volraid 10g layout=raid5 nlog=2
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
# vxassist -b -g mydg -o ordered make volraid 10g layout=raid5 \ ncol=3 nlog=2 logdisk=mydg07,mydg08 mydg04 mydg05 mydg06