Managers And Quorum - HP StoreVirtual 4000 User Manual

For more information about managers, see
Table 38 Default number of managers added when a management group is created
Number of storage systems
1
2
3
4
5 or more
1
See "Failover Managers" (page 120)
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 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—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 39 Managers and fault tolerance
Number of managers
1
2
3
4
5
"Managers overview" (page
Manager configuration
1 manager
2 managers and a virtual manager, if a Failover Manager
is not available.
3 managers
3 managers
5 managers
and "Virtual Managers" (page 120)
Table 39 (page
Fault tolerance
None
None
High
High
High
118).
1
2
for more information about virtual managers
119).
Explanation
If the manager fails, no data
control takes place. This
configuration is not
recommended.
An even number of
managers is not
recommended, except in
specific configurations.
Contact HP Support for more
information.
If one manager fails, two
remain to maintain quorum.
However, two managers do
not provide fault tolerance.
An even number of
managers is not
recommended, except in
specific configurations.
Contact HP Support for more
information.
If one or two managers fail,
three remain to maintain
quorum.
Managers overview 1 19