A.1.2 Number of Classes

PRIMECLUSTER Global Disk Services Configuration and Administration Guide 4.2 (Linux)

The number of root classes [Itanium] you can create for one node is limited to one.

There is no limit to the number of local classes [Linux2.6] and shared classes.

Separate classes conforming to the following rules.

Register system disks with a root class. [Itanium]
It is recommended to register local disks other than system disks (disks used on one node) with local classes, but not with a root class, to differentiate the local disks from the system disks in management. [Linux2.6]
Register shared disks in a cluster system (disks used from multiple nodes in the cluster) with shared classes.
In a cluster system, register shared disks whose scopes (groups of sharing nodes) are different with separate shared classes.
In a cluster system, for applications to use shared disks, create one or more shared classes with respect to each cluster application.
Divide the class if the number of created disks or volumes in a class exceeds the limit. For the numbers of disks and volumes, see "Number of Disks" and "Number of Volumes."
In a large-scale system to which numerous disk units are connected, separating classes based on physical configurations and data contents of disks may bring higher manageability.
When a disk unit is expanded, unless the rules above apply, register expanded disks to existing classes. Creating new classes is not required.

Do not separate classes more than necessary. Keeping the number of classes to a minimum will offer the following advantages.

If a class includes more disks, the probability that GDS configuration information stored on disks is lost due to disk failure will be lower. Therefore, not separating classes more than necessary to increase the number of disks within one class will raise system reliability.
In a cluster system, if there are less shared classes, it takes shorter time to switch nodes.
If there are fewer classes, less memory resources will be required.