Managers Overview; Functions Of Managers; Managers And Quorum - HP StorageWorks P4000 User Manual

Number of storage systems
2
3 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 35 Managers and quorum
Number of
Managers
1
2
3
Number for Fault toler-
a quorum ance
1 None
2 None
2 High
Manager configuration
2 managers and a Virtual Manager
3 managers
Table 35 on page 149.
Explanation
If the manager fails, no data control takes place. This arrange-
ment is not recommended.
Even number of managers not recommended, except in
specific configurations. Contact Customer Support for more
information.
If one manager fails, 2 remain, so there is still a quorum.
(Note: 2 managers are not fault tolerant. See above.)
P4000 SAN Solution user guide 149