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Re: [Linux-cluster] Fencing agents



Adam Manthei пишет:

On Wed, Aug 03, 2005 at 11:58:47AM +0000, "Sævaldur Arnar Gunnarsson [Hugsmiðjan]" wrote:


I'm implementing a shared storage between multiple (2 at the moment) Blade machines (Dell PowerEdge 1855) running RHEL4 ES connected to a EMC AX100 through FC.

The SAN has two FC ports so the need for a FC Switch has not yet come however we will add other Blades in the coming months.
The one thing I haven't got figured out with GFS and the Cluster-Suite is the whole idea about fencing.



Funny timing :) I just checked in the fencing agent for the PowerEdge
1855's a couple days ago!


(http://sources.redhat.com/cgi-bin/cvsweb.cgi/cluster/fence/agents/drac/fence_drac.pl?rev=1.3.4.2&content-type=text/x-cvsweb-markup&cvsroot=cluster)



The fencing agents in that setup is manual fencing.



I would strongly discourage this.



What does "automatic" fencing have to offer that the manual fencing lacks.
If we decide to buy the FC switch right away is it recomended that we buy one of the ones that have fencing agent available for the Cluster-Suite ?



In this case, you already have a fencing agent (fence_drac) that works with the PE 1855 blades so there is no need for further fencing hardware (unless you are going to be connecting other machines to the cluster that aren't going to have any other form of fencing)

The main advantage that "automatic" fencing gives you over manual fencing is
that in the event that a fencing operation is required, your cluster can
automatically recover (on the order of seconds to minutes) instead of waiting
for user intervention (which can take minutes to hours to days depending on
how attentive the admins are :).




"recover"? You mean reboot? But if a machine need fencing, doesn't that mean that something is inherently wrong with that machine and simple reboot would't cure that?


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