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Re: [Cluster-devel] RFC: generic improvement to fence agents api



On 03/19/2011 02:34 AM, Fabio M. Di Nitto wrote:
> Hi all,
> 
> while discussing on linux-cluster the support of the Tripp Lite switched
> PDU, it occurred to me that we can effectively improve (almost half) the
> time it takes to perform power fencing of certain devices, when for
> example, more than one PSU needs to be powered off to complete the action.
> 
> Node X has 2 PSU.
> 
> In our current state, the config would look like:
> 
> <clusternode .....>
>  <fence>
>   <method...>
>    <device name="..." port="1"/>
>    <device name="..." port="2"/>
> .....
> 
> it means effectively spawning, most likely the same agent, twice.
> Increasing the time it takes to fence and maybe increasing the
> possibility to fail to fence if the second connection fails.
> 
> My suggestion would be to allow to specify a list of ports instead.
> 
> <clusternode .....>
>  <fence>
>   <method...>
>    <device name="..." ports="1 2"/>
> ....
> 
> Either by using a new keyword "ports" or re-using "port" itself. If
> using "port", current configuration will continue to work as-is and the
> change effectively would not introduce any backward compatibility issue.
> 
> This way the agent can:
> 
> 1) connect once (reducing in most cases the ssh/telnet/whatever time)
> 2) issue the OFF command as fast as possible (almost in parallel)
> 3) then wait for the results.
> 
> By adopting a list, the configuration would look cleaner too IMHO.
> 
> A quick glance, the change should not affect fenced (David can you
> confirm please?), and most agents could handle it via the fencing python
> lib (Marek?).
> 
> Does it sound reasonable?
> 
> Cheers
> Fabio

I like this idea, but would like to suggest:

* Keep 'port' for a single port, as it is, and add 'ports' for multiple
port definitions.
* When using ports, I'd recommend comma-separated values and
dash-separated ranges (ie: ports="1,2", ports="1-4", ports="1,3-5") and
combinations there-of. This strikes me as more "standard" and possibly
less prone to typos.

-- 
Digimer
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