[Linux-cluster] Tripp Lite switched PDU fence agent; exists?

[bergman at merctech.com]

The pithy ruminations from "Fabio M. Di Nitto" <fdinitto at redhat.com> on "Re: [Linux-cluster] Tripp Lite switched PDU fence agent; exists?" were:


=> 
=> Wouldn´t it be possible for the agent to:
=> 
=> 1) issue OFF command
=> 2) either poll for OFF status or wait > $known_random_max_delay
=> 3) issue ON command
=> 4) profit?


Yes, but here's the problem:

	0) there's a condition whereby cluster communication is lost between nodeA and nodeB
	1) the agent on nodeA sends OFF command to PDU to shut down nodeB
	2) the agent on nodeA polls for OFF status while waiting > $known_random_max_delay
	3) the agent on nodeB sends OFF command to PDU to shut down nodeA
	4) nodeB shuts down
	5) nodeA shuts down

The PDU responds quickly to network connections (ie., telnet & commands to shut down a power outlet). The PDU accepts multiple network sessions (ie., from nodeA and nodeB). The PDU delays executing the commands, potentially leaving enough time for multiple nodes to send commands each to shut down the "other" node.

Mark

=> 
=> even if it takes time to fence, it would make it usable.
=> 
=> Not all fence devices are millisecond fast either...
=> 
=> Fabio
=> 
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