11.0 HP StoreVirtual Storage User Guide (AX696-96275, December 2013)

For more information about managers, see “Managers overview” (page 118).
Table 41 Default number of managers added when a management group is created
Manager configurationNumber of storage
systems
1 manager1
2 managers and a virtual manager, if a Failover Manager is not available.
1
2
3 managers3
3 managers4
5 managers
2
5 or more
1
See “Failover Managers” (page 120) and “Virtual Managers” (page 120) for more information about virtual managers
and Failover Managers.
2
Management groups are not permitted to have more than 5 managers. If you want to add a special manager (e.g.,
Failover Manager) and already have 5 managers, you must first stop a regular manager and then add the special
manager. Alarms will be displayed for management groups that are not running the correct number of managers. To
resolve the alarm, ensure the correct number of managers are configured for the management group.
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 for
the LeftHand OS 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—half of the managers do not agree with the other half. This state, known as “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 42 (page 119).
Table 42 Managers and fault tolerance
ExplanationFault
tolerance
Number of
managers
If the manager fails, no data control takes place. This configuration is not recommended.None1
An even number of managers is not recommended, except in specific configurations.
Contact HP Support for more information.
None2
If one manager fails, two remain to maintain quorum. However, two managers do not
provide fault tolerance.
High3
An even number of managers is not recommended, except in specific configurations.
Contact HP Support for more information.
High4
If one or two managers fail, three remain to maintain quorum.High5
Regular managers and specialized managers
Regular managers run on storage systems in a management group. The LeftHand OS software has
two types of specialized managers, Failover Managers and virtual managers. You can only use
one type of specialized manager in a management group. The Failover Manager is recommended
for management groups with a single, two-system cluster, and in Multi-Site cluster configurations
with two clusters. When using the Management Group wizard, the virtual manager is automatically
added to two-system configurations if a Failover Manager is not added. However, the Failover
Manager is the recommended solution for maintaining fault-tolerance on the SAN.
Managers overview 119