[Linux-cluster] How does disk prevent split brain?

[Rick Rodgers]

Thanks for the info. Yes I understand what you are saying. However, if 
you do not specify and ip-tiebreaker I assumed it used the disk tiebreaker
by default.

----- Original Message ----
From: Lon Hohberger <lhh at redhat.com>
To: linux clustering <linux-cluster at redhat.com>
Sent: Monday, October 2, 2006 9:20:14 AM
Subject: Re: [Linux-cluster] How does disk prevent split brain?

On Sun, 2006-10-01 at 20:59 -0700, Rick Rodgers wrote:
> According to RH documentation and the engineers you can have a safe
> two node 
> cluster without having to have an ip-tiebreaker. They say it will use
> the disk tie-breaker.
> 
> How is this possible?  Since clulockd is running separately on each of
> the nodes how does
> it prevent each node from accessing the disk at the same time and
> declaring himself the 
> Active node? If it is through some sort of locking mechanism that
> insures this can you please
> be technically specific in what it is?

Only one will be the lock master, because there is knowledge that both
nodes are actually still online.

You can not disable/move services when the cluster network is dead, but
both nodes can continue running the services they already are running.
Most people should probably use the disk tiebreaker if they want
failover if a node's cluster network gets disconnected.

-- Lon


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