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Donald K. Burleson

Oracle RAC Tips

Volume Management

The cluster volume manager is a software module that virtualizes the physical storage and presents the usable entities for the applications, such as the database at the operating system level. It is a storage administrator layer at the host level.

The Veritas cluster volume manager (CVM) uses objects for storage management. The two types of objects used by Volume Manager are physical objects and virtual objects.

  • Physical objects – Volume Manager uses two physical objects: physical disks and partitions. Partitions are created on the physical disks (on systems that use partitions).
     

  • Virtual objects - Volume Manager creates virtual objects, called volumes. Each volume records and retrieves data from one or more physical disks. A volume is a virtual disk device that appears to applications, databases, and file systems as a physical disk. Volumes are also composed of other virtual objects such as ‘sub-disks’ and ‘plexes’. These are used to change volume configuration features such as concatenation, mirroring, and striping. Volumes and their virtual components are called virtual objects.

Volume management involves using physical disks or LUNS to create disk groups. These disks are combined to create volumes with a layout or configuration appropriate to their purpose, for example, mirroring or striping etc. The volumes are flexible objects that can easily be extended or modified. The volume management operations include:

  • Placing the shared disks or LUNS from the shared storage array into the Volume Manage control. When the LUNS are placed under the VM control, they are known as VM disks

  • Creating the Disk Groups – the disk groups that contain the database application must be available to all nodes in the cluster. A disk group allows disks, volumes, and file systems that are relevant to a single database to be arranged into a logical collection for easy administration.

  • Creating volumes with the appropriate layout (mirror, stripe. etc.) and size from the disk group storage pool. Volumes are flexible objects that can be extended or modified.

  • Making file systems from the volumes and mounting them for database use. Volumes can also be used for database applications, in which case they are referred to as raw devices.

It is important to understand that volumes are the basic storage components that an Oracle database utilizes. The volumes, as created by the CVM, are accessible by all members or nodes of the cluster. This is an important distinction in the RAC environment. A volume can be accessed either directly by the RAC database as a raw partition, or through mounted file systems such as a CFS, as shown in Fig 6.8

Fig 6.8 Volume requirements for Oracle

To begin the Oracle installation using the Veritas DBE/AC, a shared disk group and the necessary volumes need to be created.

The following steps provide an example of how to create the disk group and volumes:

  1. From the master node in the cluster, create the shared disk group on the shared disk c2t3d1:

# vxdg -s init orasrv_dg c2t4d2

  1. Set the connectivity policy for the disk group as local:

# vxedit set diskdetpolicy=local orasrv_dg

  1. Create the volume in the shared disk group:

# vxassist -g orasrv_dg make srvm_vol 200M

  1. Set the activation mode to read-write:

# vxdg -g orasrv_dg set activation=sw

  1. On the other node, enter:

# vxdg -g orasrv_dg set activation=sw

  1. In order to create the cluster file system, on the other node, enter:

# vxdg -g orasrv_dg set activation=sw

  1. To create the file system on srvm_vol:

# mkfs -F vxfs /dev/vx/rdsk/orasrv_dg/srvm_vol

  1. On both systems, create the mount point for the file system:

# mkdir /orasrv

  1. On both systems, mount the file system, using the device file for the block device. Use the option flag –o cluster.

# mount -F vxfs -o cluster /dev/vx/dsk/orasrv_dg/srvm_vol /orasrv

  1. To determine which node is the master, use the command:

vxdctl -c mode

In the output, look for:

cluster active - MASTER

or:

cluster active - SLAVE

For detailed volume management commands, please refer to the Veritas volume manager manual.


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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