VERITAS Volume Manager 3.1 Administrator's Guide

Recovery
Miscellaneous RAID-5 Operations
Chapter 8382
Step 6. When all subdisks have been recovered, the volume is placed in the
ENABLED kernel state and marked as ACTIVE. It is now started.
Changing RAID-5 Volume Attributes
You can change several attributes of RAID-5 volumes. For RAID-5
volumes, the volume length and RAID-5 log length can be changed by
using the vxvol set command. To change the length of a RAID-5
volume, use the following command:
# vxvol set len=10240 r5vol
The length of a volume cannot exceed the mapped region (called the
contiguous length, or contiglen) of the RAID-5 plex. The length
cannot be extended so as to make the volume unusable. If the RAID-5
volume is active and the length is being shortened,the operation must be
forced by using the -o force usage type option. This is done to prevent
removal of space from applications using the volume.
The length of the RAID-5 logs can also be changed using the following
command:
# vxvol set loglen=2M r5vol
Remember that RAID-5 log plexes are only valid if they map the entire
length of the RAID-5 volume log length. If increasing the log length
makes any of the RAID-5 logs invalid, the operation not allowed. Also, if
the volume is not active and is dirty (not shut down cleanly), the log
length cannot be changed. This avoids the loss of any of the log contents
(if the log length is decreased) or the introduction of random data into
the logs (if the log length is being increased).
Writing to RAID-5 Arrays
This section describes the write process for RAID-5 arrays.
Read-Modify-Write
When you write to a RAID-5 array, the following procedure is used for
each stripe involved in the I/O:
Step 1. The data stripeunits to be updated with new write data areaccessed and
read into internal buffers. The parity stripe unit is read into internal
buffers.