VERITAS Storage Foundation 4.1 for Oracle RAC HP Serviceguard Storage Management Suite Extracts, December 2005

Storage Foundation for Oracle RAC Communications
Group Membership Services/Atomic Broadcast (GAB)
GAB is responsible for Cluster Membership and Cluster Communications as described
below.
Cluster Membership
All nodes in a distributed system, such as Storage Foundation for Oracle RAC, must be
aware of each node currently participating in the cluster. Nodes can leave or join the
cluster because of shutting down, starting up, rebooting, powering off, or faulting
processes.
Storage Foundation for Oracle RAC uses LLT heartbeats to determine cluster membership.
When systems no longer receive heartbeats from a peer for a predetermined interval, a
protocol excludes the peer from the current membership. When systems start receiving
heartbeats from a peer that is not part of the membership, a protocol enables the peer to
join the current membership.
Storage Foundation for Oracle RAC delivers the new membership information consistently
to all nodes and initiates actions specific to each module. For example, if a node faults,
CVM initiates volume recovery and CFS performs a parallel file system check.
Cluster Communications
The second function of GAB is to provide reliable cluster communications for Storage
Foundation for Oracle RAC modules. GAB provides guaranteed delivery of point-to-point
messages and broadcast messages to all nodes. Point-to-point messaging involves sending
and acknowledging the message. Atomic-broadcast messaging ensures all systems within
the cluster receive all messages. If a failure occurs while transmitting a broadcast message,
GAB ensures all systems have the same information after recovery.
.
GAB Messaging
- Cluster Membership/State
Server
Server
NICNIC
NIC NIC
- Datafile Management
- File System Metadata
- Volume Management
Chapter 1, Overview: Storage Foundation for Oracle RAC 7