HP StoreVirtual 4000 9.0 HP StorageWorks P4000 SAN Solution User Guide - Page 149
Managers overview, Functions of managers, Managers and quorum
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Number of storage systems 2 3 or more Manager configuration 2 managers and a Virtual Manager 3 managers 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 on page 149. Table 35 Managers and quorum Number of Number for Fault tolerManagers a quorum ance 1 1 None 2 2 None 3 2 High Explanation If the manager fails, no data control takes place. This arrangement 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