Suppose a 2 nodes VCS HA environment have 2 local heartbeats. As per my understanding VCS dont need IP addresses for its local heartbeats communication and uses its own protocol(LLT) for heartbeats between both HA nodes.
My question is, if we assign an IP address on one heartbeat NIC and connect a ip device back to back, Can we allow to do it ?
Technically yes you can do it although it is not recommended for a failover VCS configuration.
As Veritas cluster requires minimum two dedicated NICs for cluster inter node heartbeat (primarily) communicaton on dedicated private network meaning if an IP is plumbed on a private NIC, only the nodes in the cluster can use this IP for sending/receiving network packets. For testing purpose, its perfectly OK to plumb an IP on one or both NICs.
However if you think of transmiting large amount of data through these NICs via LLT private network, it is not recommended. When the large amount of packets is transmitted through the LLT network, it may results cluster nodes miss heartbeat and errors like node inactive/in trouble may be resulted.
For CVM/CFS/RAC clusters, they are different and beyond the scope of this discussion.
Agreed that 2 LLT heartbeats and one low priority heartbeat is an ideal scenario. Additionally, I can understand that price for NIC & switch is small but actually the hardware are blade servers and no provision to add additional NIC in it.
To ensure reliability of cluster on a one LLT heartbeat and one low priority heartbeat, can we configure SAN BASED FENCING on top of one LLT heartbeat and one low priority heartbeat cluster ?