> -----Original Message-----
> From: Digimer [mailto:lists@xxxxxxxxxx]
> Sent: Monday, June 16, 2014 3:20 PM
> To: CentOS mailing list
> Subject: Re: Question about clustering
>
> On 16/06/14 02:55 PM, m.roth@xxxxxxxxx wrote:
<SNIP>
> > One can also set the cluster nodes to failover, and when the failed node
> > comes up, to *not* try to take back the services, leaving it in a state
> > for you to fix it.
> >
> > mark, first work on h/a clusters 1997-2001
>
> Failover and recovery are secondary to fencing. The surviving node(s)
> can't begin recovery until the lost node is in a known state. To make an
> assumption about the node's state (by, for example, assuming that no
> access to the node is sufficient to determine it is off) is to risk a
> split-brain. Even something as relatively "minor" as a floating IP can
> potentially cause problems with ARP, for example.
>
> Cheers
Having operated a file serving cluster for a few years (~2001-2006) without ANY fencing device, I can tell you that it causes split-brain in the admins too, i.e., I AGREE.
Earlier, Alessandro Baggi wrote:
> there is a chance to make fencing without hardware, but only software?
To which Digimer, answered: No. <SNIP info about fence device independence>
However, there is an *Almost* software only fence.
Unfortunately for me I learned about (or at least understood) the stonith devices late in the above system's life. I expect even meatware stonith[1] could have saved me considerable pain five or six times.
Understand that I am not recommending meatware stonith to be a good operational stonith device, see [2] for how much subtle understanding the meat has to have, but it would be much better than NO operational stonith device.
[1] http://clusterlabs.org/doc/crm_fencing.html#_meatware
[2] http://oss.clusterlabs.org/pipermail/pacemaker/2011-June/010693.html
Even when this disclaimer is not here:
I am not a contracting officer. I do not have authority to make or modify the terms of any contract.
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