HP CLX Migration Whitepaper

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• Quorum Server
Quorum Server can be used as a membership arbitration method for multiple clusters at a time. The Quorum Server does
not have any limitation in terms of number of nodes in a cluster. The Quorum Server software can be configured as a
Serviceguard package, or standalone, but in either case it must run on a system outside of the cluster for which it is
providing quorum services. The Quorum Server listens to connection requests from the Serviceguard nodes on a known
port. The server maintains a special area in memory for each cluster, and when a node obtains the cluster lock, this area is
marked so that other nodes will recognize the lock as “taken.”
The Quorum Server software is available for HP-UX 11i v2, v3, Red Hat Enterprise Linux, and SUSE Linux Enterprise
Server. The Software can be downloaded free from software.hp.com. A single Quorum Server can serve multiple
Serviceguard for Linux and Serviceguard for HP-UX clusters. Ideally the Quorum Server must be configured in a separate
service cluster for High Availability in fault domain different from the fault domain of servers in the cluster serviced by
them.
• Node Fencing
A reboot is done if a cluster node cannot communicate with the majority of cluster members for the pre-determined time,
split brain or under other circumstances such as a kernel hang or failure of the cluster daemon (cmcld). This reboot is
initiated by deadman driver which act as a robust fencing mechanism in SG/LX cluster. There is no manual configuration
needed to configure deadman driver. The deadman driver is compiled into the kernel automatically when SG/LX is
installed but if you are planning to update Linux kernel then it is required to recompile the kernel with deadman driver.
Networking in the SG/LX cluster
Serviceguard for Linux uses one or more Heartbeat networks to send heartbeat among all the nodes, to maintain the cluster
membership. SG/LX also uses the Heartbeat network for communication between nodes. To build a resilient cluster it is
crucial to have resilient heartbeat network infrastructure. HP recommends to configure multiple heartbeat networks and use
Channel Bonding technologies at link level.
Applications deployed in SG/LX cluster can use their own network in the cluster, for their client access. Such networks are
called Client access networks. Serviceguard for Linux can monitor and manage IP addresses used by applications on these
networks. During failover, Serviceguard for Linux can move the application’s IP addresses on the client access network from
the failed node to the target node. You can also configure the client access networks for heartbeat network traffic. SG/LX
exchanges only small messages and does not have demanding bandwidth requirements. So using client access networks
for heartbeat also does not affect application accessibility or performance.