Using Serviceguard Extension for RAC, 7th Edition, September 2008

Building Mirrored Logical Volumes for RAC with LVM Commands
After you create volume groups and define physical volumes for use in them, you define mirrored
logical volumes for data, logs, and control files. It is recommended that you use a shell script to
issue the commands described in the next sections. The commands you use for creating logical
volumes vary slightly depending on whether you are creating logical volumes for RAC redo log
files or for use with Oracle data.
Creating Mirrored Logical Volumes for RAC Redo Logs and Control Files
Create logical volumes for use as redo log and control files by selecting mirror consistency
recovery. Use the same options as in the following example:
# lvcreate -m 1 -M n -c y -s g -n redo1.log -L 28 /dev/vg_ops
The -m 1 option specifies single mirroring; the -M n option ensures that mirror write cache
recovery is set off; the -c y means that mirror consistency recovery is enabled; the -s g means
that mirroring is PVG-strict, that is, it occurs between different physical volume groups; the -n
redo1.log option lets you specify the name of the logical volume; and the -L 28 option allocates
28 megabytes.
NOTE: It is important to use the -c y options for both redo logs and control files. These options
allow the redo log files to be resynchronized by SLVM following a system crash before Oracle
recovery proceeds. If these options are not set correctly, you may not be able to continue with
database recovery.
If the command is successful, the system will display messages like the following:
Logical volume “/dev/vg_ops/redo1.log” has been successfully created
with character device “/dev/vg_ops/rredo1.log”
Logical volume “/dev/vg_ops/redo1.log” has been successfully extended
NOTE: The character device file name (also called the raw logical volume name) is used by the
Oracle DBA in building the RAC database.
Creating Mirrored Logical Volumes for RAC Data Files
Following a system crash, the mirrored logical volumes need to be resynchronized, which is
known as “resilvering”.
On node and cluster wide failures, when SLVM mirroring is used and Oracle resilvering is
available, the recommendation for the logical volume mirror recovery policy is set to either full
mirror resynchronization (NOMWC) or fast resynchronization (MWC) for control and redo files
and no mirror resynchronization (NONE) for the datafiles since Oracle would perform resilvering
on the datafiles based on the redo log.
If Oracle does not perform “resilvering” of RAC data files that are mirrored logical volumes,
choose a mirror consistency policy of “NOMWC”. This is done by disabling mirror write caching
and enabling mirror consistency recovery. With “NOMWC”, SLVM performs the
resynchronization.
NOTE: If Oracle resilvering is not available, the mirror recovery policy should be set to either
full mirror resynchronization (NOMWC) or fast resynchronization (MWC) of all control, redo,
and datafiles. For more information on using NOMWC and MWC, refer to the HP-UX System
Administrator's Guide: Logical Volume Management HP-UX 11i Version 3 on
http://docs.hp.com
Create logical volumes for use as Oracle data files by using the same options as in the following
example:
# lvcreate -m 1 -M n -c y -s g -n system.dbf -L 408 /dev/vg_ops
Creating a Storage Infrastructure with LVM 45