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Single network link and reliability

Certain environments may prefer using a single private link or a pubic 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. Note that these nodes start in jeopardy state, as described in I/O fencing. I/O fencing is used to handle split-brain scenarios. The option for single network is given during installation.

Low priority 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

# lltconfig -d device -t tag

 To remove a link

# lltconfig -u tag

Changes take effect immediately and are lost on the next reboot. For changes to span reboots you must also update /etc/llttab.


  Note   LLT clients do not recognize the difference unless only one link is available and GAB declares jeopardy.