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About shared disk groups

Make sure you review the following general information when dealing with disk groups and volumes. Refer to the Veritas Volume Manager Administrator's Guide for complete details on creating and managing shared disk groups.

Viewing information on a disk group

To display information about a specific disk group, type:

vxdg list disk_group

Checking the connectivity policy on a shared disk group

By default, the connectivity policy for a shared disk group is set to "global." This setting protects against possible data corruption and causes all nodes in the cluster to detach from the disk group when any node reports a disk failure.

The output of the vxdg list shared_disk_group command includes the following line:

detach-policy: global

To change the connectivity policy for a disk group from "local" to "global," type:

# vxedit set diskdetpolicy=global shared_disk_group

Determining whether a node is CVM master or slave

On one node (nebula), determine whether the node is the master or slave:

# vxdctl -c mode

On nebula, which is the slave, the output shows:

mode: enabled: cluster active - SLAVE

master: galaxy

On galaxy, which is the master, the output shows:

mode: enabled: cluster active - MASTER

master:galaxy

Enabling write access to volumes in the disk groups

By default, the activation mode for shared disk groups is inactive (set to off). To create databases on the shared volumes, enable the write access to the volumes:

On the CVM master node, enter:

vxdg -s import shared_disk_group

vxvol -g shared_disk_group startall

vxdg -g shared_disk_group set activation=sw

On the slave nodes, enter:

vxdg -g shared_disk_group set activation=sw

Refer to the description of disk group activation modes in the Veritas Volume Manager Administrator's Guide for more information.

Deporting and importing shared disk groups

Shared disk groups in an SF Oracle RAC environment are configured for "Autoimport" at the time of CVM startup. If the user manually deports the shared disk group on the CVM master, the disk group is deported on all nodes. To reimport the disk group, the user must import the disk group as a shared group from the CVM master.

To deport a shared disk group, use the following command on the CVM master:

vxdg deport shared_disk_group

To import a shared disk group, use the following command on the CVM master:

vxdg -s import shared_disk_group

To import a disk group as a standalone disk group, deport it from the CVM master and use the following command on any node:

vxdg -C import shared_disk_group

To reimport a disk group as a shared disk group, deport it from the standalone node and use the following command on the CVM master node:

vxdg -C -s import shared_disk_group

Reviewing limitations of shared disk groups

The cluster functionality of VxVM (CVM) does not support RAID-5 volumes or task monitoring for shared disk groups in a cluster. These features can function in private disk groups attached to specific nodes of a cluster. Online relayout is available provided it does not involve RAID-5 volumes.

The boot disk group (usually aliased as bootdg) is a private group that cannot be shared in a cluster.

CVM only provides access to raw device; it does not support shared access to file systems in shared volumes unless you install and configure the appropriate software, such as Veritas Cluster File System (CFS). If a shared disk group contains unsupported objects, deport the group and reimport it as a private group on any node. Reorganize the volumes into layouts supported for shared disk groups, and then deport and reimport the group as a shared one.