[CentOS] Question about clustering

Tue Jun 17 14:23:33 UTC 2014
Denniston, Todd A CIV NAVSURFWARCENDIV Crane <todd.denniston at navy.mil>

> -----Original Message-----
> From: Digimer [mailto:lists at alteeve.ca]
> Sent: Monday, June 16, 2014 3:20 PM
> To: CentOS mailing list
> Subject: Re: [CentOS] Question about clustering
> On 16/06/14 02:55 PM, m.roth at 5-cent.us wrote:
> > 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

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I am not a contracting officer. I do not have authority to make or modify the terms of any contract.