Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

If there is a failure of all configured high priority links, LLT will switch all cluster
communications traffic to the first available low priority link. Communication
traffic will revert back to the high priority links as soon as they become available.
While not required, best practice recommends to configure at least one low priority
link, and to configure two high priority links on dedicated cluster interconnects
to provide redundancy in the communications path. Low priority links are typically
configured on the public or administrative network.
If you use different media speed for the private NICs, Symantec recommends that
you configure the NICs with lesser speed as low-priority links to enhance LLT
performance. With this setting, LLT does active-passive load balancing across the
private links. At the time of configuration and failover, LLT automatically chooses
the link with high-priority as the active link and uses the low-priority links only
when a high-priority link fails.
LLT sends packets on all the configured links in weighted round-robin manner.
LLT uses the linkburst parameter which represents the number of back-to-back
packets that LLT sends on a link before the next link is chosen. In addition to the
default weighted round-robin based load balancing, LLT also provides
destination-based load balancing. LLT implements destination-based load
balancing where the LLT link is chosen based on the destination node id and the
port. With destination-based load balancing, LLT sends all the packets of a
particular destination on a link. However, a potential problem with the
destination-based load balancing approach is that LLT may not fully utilize the
available links if the ports have dissimilar traffic. Symantec recommends
destination-based load balancing when the setup has more than two cluster nodes
and more active LLT ports. You must manually configure destination-based load
balancing for your cluster to set up the port to LLT link mapping.
See “Configuring destination-based load balancing for LLT” on page 102.
LLT on startup sends broadcast packets with LLT node id and cluster id information
onto the LAN to discover any node in the network that has same node id and
cluster id pair. Each node in the network replies to this broadcast message with
its cluster id, node id, and node name.
LLT on the original node does not start and gives appropriate error in the following
cases:
■ LLT on any other node in the same network is running with the same node id
and cluster id pair that it owns.
■ LLT on the original node receives response from a node that does not have a
node name entry in the /etc/llthosts file.
27Overview of Veritas Storage Foundation for Oracle RAC
Component products and processes of SF Oracle RAC