9.5.01 HP P4000 SAN Solution User Guide (AX696-96168, February 2012)

in the management group. For more information on using the map view tools, see “Using the Map
View ” (page 14).
Best practice for managers in a management group
When creating a management group, the wizard creates an optimal manager configuration for
the number of storage systems used to create the group. See Table 32 (page 107) for the default
manager configurations.
After you have finished creating the management group, be certain to reconfigure managers as
necessary to optimize your particular SAN configuration. The Best Practice analyzer for the
management group indicates if the manager configuration is satisfactory. For more information
about managers, see “Managers overview” (page 107).
Table 32 Default number of managers added when a management group is created
Manager configurationNumber of storage systems
1 manager1
2 managers and a Virtual Manager2
3 managers3 or more
Managers overview
Within a management group, managers are storage systems that govern the activity of all of the
storage systems in the group. All storage systems contain the management software, but you must
designate which storage systems run that software by starting managers on them. These storage
systems then “run” managers, much as a PC runs various services.
Functions of managers
Managers have the following functions:
• Control data replication. (Note: managers are not directly in the data path.)
• Manage communication between storage systems in the cluster.
• Resynchronize data when storage systems change states.
• Coordinate reconfigurations as storage systems are brought up and taken off line.
One storage system has the coordinating manager. You can determine which storage system
is the coordinating manager by selecting the management group, then clicking the Details
tab. The Status field at the top shows the coordinating manager.
Managers and quorum
Managers use a voting algorithm to coordinate storage system behavior. In this voting algorithm,
a strict majority of managers (a quorum) must be running and communicating with each other in
order for the SAN/iQ software to function. An odd number of managers is recommended to ensure
that a majority is easily maintained. An even number of managers can get into a state where no
majority exists—one-half of the managers do not agree with the other one-half. This state, known
as a “split-brain,” may cause the management group to become unavailable.
For optimal fault tolerance in a single-site configuration, you should have 3 or 5 managers in your
management group to provide the best balance between fault tolerance and performance. The
maximum supported number of managers is 5. See Table 33 (page 108).
Managers overview 107