Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

Single network link and reliability
Certain environments may prefer using a single private link or a public network
for connecting nodes in a cluster, despite the loss of redundancy for dealing with
network failures. The benefits of this approach include simpler hardware topology
and lower costs; however, there is obviously a tradeoff with high availability.
For the above environments, SFCFS provides the option of a single private link,
or using the public network as the private link if I/O fencing is present. I/O fencing
is used to handle split-brain scenarios. The option for single network is given
during installation.
See “About preventing data corruption with I/O fencing” on page 31.
Configuring low priority a link
LLT can be configured to use a low-priority network link as a backup to normal
heartbeat channels. Low-priority links are typically configured on the customer’s
public or administrative network. This typically results in a completely different
network infrastructure than the cluster private interconnect, and reduces the
chance of a single point of failure bringing down all links. The low-priority link
is not used for cluster membership traffic until it is the only remaining link. In
normal operation, the low-priority link carries only heartbeat traffic for cluster
membership and link state maintenance. The frequency of heartbeats drops 50
percent to reduce network overhead. When the low-priority link is the only
remaining network link, LLT also switches over all cluster status traffic. Following
repair of any configured private link, LLT returns cluster status traffic to the
high-priority link.
LLT links can be added or removed while clients are connected. Shutting down
GAB or the high-availability daemon, had, is not required.
To add a link
■ To add a link, type the following command:
# lltconfig -d device -t device_tag
where device_tag is a tag to identify particular link in subsequent commands,
and is displayed by lltstat(1M).
To remove a link
■ To remove a link, type the following command:
# lltconfig -u device_tag
See the lltconfig(1M) manual page.
29Storage Foundation Cluster File System architecture
Single network link and reliability