On Fri, 2007-10-26 at 08:21 -0700, Scott Becker wrote: > In the FAQ, Fencing Questions > 13. What's the right way to configure fencing when I have redundant > power supplies? > > I'm going to setup the second example. > My concern is about a race condition with the two devices: > > <device name="pwr01" option="off" switch="1" port="1"/> > <device name="pwr02" option="off" switch="1" port="1"/> > If I had only one power switch, the first node to login successfully > turns the other off (APC with one IP address). My concern is with two > APCs, that whoever loses the race to login to APC #1 may win the race > to login to APC #2 and then each will turn off only one of the other's > power supplies. If it fails to log in to power supply #1, fencing has failed, and it doesn't bother trying fencing option #2. It then pauses for several seconds before retrying. It's not an "either-or" situation. Both have to complete - in sequence & successfully - or fencing has failed and the entire operation must be retried. > Is the fencing execution script designed to 1) perform all necessary > fencing device logins successfully then and only then 2) issue the > poweroff commands? Thereby averting a potential race because the loser > of the race for APC #1 will give up and hand over device #2. In the absolute worst case (which I think is very, very unlikely): node1 powers off node2-PS1 node2 fails to log in to SW1 . node2 waits a bit . node2 powers off node1-PS1 node1 powers off node2-PS1 Also, note that the "fence race" case typically applies in a partition of the cluster network where fencing is still accessible. This configuration is not recommended for two node clusters; it's recommended that the cluster communicates and fences over the same network: http://sources.redhat.com/cluster/faq.html#two_node_correct Basically, the theory goes like this: If you pull the ethernet cable on a node and the fence device controlling the other node is on the same path, it will have some difficulty accessing the fence device, and will usually lose the "fence race". -- Lon -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
