Volume Groups Question

[Waqar Razi]

What is the difference between activating volume groups in exclusive mode versus shared mode? When are they used? What are the considerations in their implementation?

[Tim Nelson]

Shared mode is for MC Service Guard.

Active / Passive sharing of disk devices and their configuration.

If you do not use SG then exclusive is the default.

[SKR_1]

You can read attached PDF for refernce.

May help you.

Thanks

SKR

[Grayh]

SLVM is a mechanism that permits multiple systems in an MC/LockManager cluster to share (read/write) disk resources in the form of volume groups. The objective is a highly available system by providing direct access to disks from multiple nodes and by supporting mirrored disks, thereby eliminating single points of failure.

SLVM permits a two system cluster to have read/write access to a volume group by activating the volume group in shared mode.

SLVM is designed to be used only by specialized distributed applications (such as Oracle Parallel Server) that use raw access to disks, rather than going through a file system. The applications must provide their own concurrency control for their data, as well as transaction logging and recovery facilities, as appropriate. Applications that are not network aware, such as file systems, will not be supported on volume groups activated in shared mode.

SLVM requires services provided by MC/LockManager and thus only clusters that have MC/LockManager will be able to use shared activation.

The following commands have been modified to support SLVM requirements:

*

vgchange

The first release of 10.0 supported the "a -e" activation mode or exclusive mode. ********(Exclusive mode permits only one of the two nodes to have read /write access to the volume group the other may have read access but not read/write access.)********

For 10.10, vgchange has been modified to support the shared activation mode. It now has the "-c y -S y" option to mark the attributes of the volume group as shareable and the "-a s" option to the activate the volume group in shared mode.
*

vgdisplay vgdisplay will show the current activation mode.

[Prashanth Waugh]

Hi Razi,


If ur doing
#vgchange -a e

This is for activating vg in exclusive mode
means only one node can read/write/access to that Vg.

#vgchange -a s
this is for activating vg in share mode so more than one node read/write/access it

Regards
Atul