Using Serviceguard Extension for RAC, 6th Edition, April 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 -M n and -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”.
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.
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
58 Serviceguard Configuration for Oracle 10g RAC