HP Instant Capacity Version 10.x User Guide (5900-1581, March 2011)

Reinstalling a Group Member
If a group member is reignited, use the icapmanage command as follows to reestablish
communication between the newly ignited group member and the Group Manager:
icapmanage -a -m <member>:<host> -g <group_name>
See the HP Instant Capacity Release Notes for more details about reestablishing SSL certificates.
Group Manager Availability (No Standby Manager)
If the active Group Manager becomes unavailable and a standby Group Manager is not defined
or not used, management of the GiCAP group is unavailable until the Group Manager is restored
or replaced. The GiCAP group members continue to operate as isolated Instant Capacity systems,
using whatever usage rights and temporary capacity they had available when the Group Manager
became unavailable. A GiCAP group member using borrowed usage rights can continue using
those usage rights. A GiCAP group member that has loaned usage rights to other members in the
GiCAP group cannot recover those usage rights until the Group Manager is restored.
If a standby Group Manager is not used, loaned and borrowed usage rights remain in place in
GiCAP group members when the active Group Manager is unavailable. All usage rights held by
the Group Manager itself are left unavailable until the Group Manager is restored.
Normally, usage rights are not held by the Group Manager, but this can occur after a member is
removed from a GiCAP group, or if the Group Manager becomes unavailable during the transfer
of usage rights from one GiCAP group member to another.
Group Manager Failover Considerations
If the active Group Manager system becomes unavailable and a standby Group Manager has
previously been defined, the standby Group Manager can be used to take over GiCAP group
operations from the Group Manager. If both the active Group Manager and the standby Group
Manager are unavailable, or if the active Group Manager fails and the administrator chooses not
to have the standby Group Manager take over group operations, then the usage rights and
temporary capacity remain as per allocated to each group member, as described in the previous
section “Group Manager Availability (No Standby Manager)” (page 82).
However, if a standby Group Manager has been defined, an administrator can have a standby
Group Manager take control at any time using the icapmanage -Q command. While this can
be done routinely, for example to allow shutting down a functioning active Group Manager for
maintenance, normally this command is issued either when the active Group Manager has failed,
or when a network outage has made it unable to communicate with critical group members. When
a standby manager is told to take control, it attempts to update all members and the current active
Group Manager so that group operations can proceed smoothly.
However, in the case of a failure, it is possible that the icapmanage -Q command is unable to
contact the active Group Manager and some members of the groups that it now manages. When
this happens, the previously active Group Manager remains active, unaware of the change of
control. This is referred to as a “bifurcated” (or “split”) GiCAP group. Members that were reachable
by the standby Group Manager when it took control cannot accept commands from the old active
Group Manager; but unreachable members continue to consider it active. Control operations can
be carried out on both active Group Managers, each communicating with the members that it (and
only it) can reach. Groups and members can be added or removed on both (subject to the set of
members each can command), and sharing rights can be added on both. In some cases this can
be valuable; for example, when two data centers each remain functional but some intervening
network link has been broken. Each isolated set of systems can proceed with independent disaster
recovery operations within their group subset.
At some point, communication is restored and the split groups must be rejoined. This is accomplished
through issuing new icapmanage -Q command. It can be executed on either active Group
Manager to confirm that Group Manager as the active Group Manager and demote the other to
82 Global Instant Capacity