[Linux-cluster] Fencing Race Question

[Chris Harms]

We have our APC power strips group the 2 ports together. The fence agent 
should login to only one IP and turn off the grouped ports instead of 
logging in to each unit separately to turn off power.


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.
>
> 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.
>
>     thanks
>     newby
>     scottb
>
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