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Donald K. Burleson

Oracle RAC Tips

Veritas Cluster Volume Management

The Veritas Volume Management (VxVM) tool manages physical disks and presents logical disks for application use. Logical disks are known as volumes. A volume is the disk space that appears to the database as a physical partition. VxVM operates as a sub-system between the operating system and the database system.

We need to create one or more shared disk groups besides the rootdg disk group. rootdg must exist and cannot be shared between the systems. At least one disk must be in the rootdg disk group. The shared disk group is accessible for all the nodes in the cluster.

The cluster functionality of a VxVM works together with the cluster manager daemon. The CM informs VxVM of the changes in cluster membership based on which access is controlled. When a node joins a cluster it gains access to shared disks. When a node leaves a cluster it no longer has access to shared disks. A node joins a cluster when the cluster manager is started on that node.

To the cluster manager, all nodes are the same. All nodes that join the cluster can potentially access VxVM objects configured within shared disk groups. However, the cluster functionality of VxVM requires that one node act as the master node. All other nodes in the cluster are slave nodes. Any node is capable of being the master node and it is responsible for coordinating certain VxVM activities.

We must run all the commands that configure or reconfigure VxVM objects on the master node. Tasks that must be initiated from the master node include setting up shared disk groups, creating and reconfiguring volumes, and performing snapshot operations. VxVM determines that the first node to join a cluster performs the function of master node. If the master node leaves a cluster, one of the slave nodes is chosen to be the new master.

There are three interfaces to use with the volume manager:

  • Volume Manager Storage Administrator (VMSA) is a graphical user interface to Volume Manager.

  • Command Line Interface (CLI): The command line interface (CLI) consists of UNIX utilities that are invoked from the command line to perform Volume Manager and standard UNIX tasks. You can use the CLI not only to manipulate Volume Manager objects, but also to perform scripting and debugging functions.

  • Volume Manager Support Operations (vxdiskadm): The Volume Manager Support Operations interface, commonly known as vxdiskadm, is a menu-driven, text-based interface that you can use for disk and disk group administration functions.

Placing the physical disks into the group creates a disk group and then individual volumes can be created for the various Oracle files. Let us look at some examples.

To create a disk group called oradg over 4 LUNs:

# vxdg -s init oradg1 ora01=c1t1d0s2 ora02=c1t2d0s2 ora03=c1t3d0s2 ora04=c1t4d0s2

To create a RAID 0+1 (mirror/stripe) volume across 4 disk LUNs:

# vxassist -g oradg1 make rac_system_500m 500m layout=stripe stripeunit=256 ncolumn=4 user=oracle group=dba alloc="ora01 ora02 ora03 ora04"

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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