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Donald K. Burleson

Oracle RAC Tips

Set up Disks

Cluster servers have internal disks, which are used as emergency boot disks or additional swap space. There is a minimum of four shared disks required for setting up the cluster. In addition, you will need to have extra disks for the use of the Oracle database. Plan to have as many disks as needed.

Create the mount point for the Oracle software as the root user. For example, use dsk9 to set up the file system as shown below:

# disklabel -z dsk9
# disklabel -rw dsk9 RZ1CF-CF Oracle
# mkfdmn /dev/disk/dsk9c Oracle
# mkfset Oracle fs1
# mkdir /u01
# mount Oracle#fs1 /u01
# chown Oracle:dba /u01

Now create the file systems for the Oracle database data files. If there is sufficient room on the same disk (/u01) as the Oracle software, create a directory named /u01/oradata.

# disklabel -z dsk20
# disklabel -rw dsk20 RZ1CF-CF Oracle
# mkfdmn /dev/disk/dsk20c OracleDb
# mkfset OracleDb fs1
# mkdir /u02
# chown Oracle:dba /u02
# mount OracleDb#fs1 /u02

Add the mount lines to /etc/fstab.

Oracle#fs1 /u01 advfs rw 0 2
OracleDb#fs1 /u02 advfs rw 0 2

The file systems above are created and mounted as cluster file systems. Cluster File system provides a single system image for the users and applications. CFS follows a client/server model with each file system served by a cluster member.

Using Logical Volume Manager (LSM)

Instead of using the disks as they are, you can use the Logical Volume Manager to organize the disks into manageable entities. Logical Storage Manager is an integrated, host-based disk management tool that enables you to configure your storage to protect against data loss and improve disk I/O performance.

LSM builds virtual disks, called volumes, on top of the UNIX system disks. A volume is a Digital UNIX special device that contains data used by a UNIX file system, a database, or other application. LSM transparently places a volume between a physical disk and an application, which then operates on the volume rather than on the physical disk. A file system, for instance, is created on the LSM volume rather than on a physical disk.

LSM obtains space for the file system or the raw database by creating an LSM volume of the appropriate size. A volume is built from one or more areas of disk space (also called sub disks) located on one or more physical disks. This makes it possible to extend volumes by adding disk space that is not contiguous with the space already allocated, and to create volumes that exceed the size of a physical disk.

We can organize a collection of physical disks that share a common configuration or function into disk groups. LSM volumes are created within a disk group and are restricted to using disks within that disk group.

The following example of the volassist command creates a 750MB mirrored volume:

# volassist make vol01 750mb mirror=true

The following list outlines LSM support for basic cluster-wide file systems:

  • Supported: root (/), /usr, /var file systems, and member swap partitions.

  • Not supported: quorum disk and member boot disks.

For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.  


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