Re: Oracle CRS and Split Brin

I am not so sure that node 1 will be evicted! I cant unplug any cables now otherwise I would do it!

Kevin mentioned that in a split brain scenario the lower node would survive always

On 3/29/07, Naqi Mirza <naqimirza_at_yahoo.com> wrote:
>
> node1 loses its interconnect - this is where I understand the misscount
> parameter comes into play. The oracle cssd process checks for the network
> and disk heartbeat. Misscount represents the maximum time that a heartbeat
> can
> be missed before entering into a cluster reconfiguration to evict a node.
> So if node1 were to lose its interconnect (regardless of being the master it
> should be evicted shouldn't it?). This would leave one of the other(s) to
> become the new master - which one becomes the master - i guess Kevin's
> already answered that one.
> When the evicted node is back in business - i assume you mean its
> interconnect is now fixed, a cluster reconfiguration should take place
> adding that node back into the cluster.
> I'm sure once Kevin has a glance over this he'll correct me where I'm
> wrong.
>
> Naqi
>
> ----- Original Message ----
> From: amonte <ax.mount_at_gmail.com>
> To: Kevin Closson <kevinc_at_polyserve.com>
> Cc: naqimirza_at_yahoo.com; oracle-l_at_freelists.org
> Sent: Thursday, 29 March, 2007 4:32:02 AM
> Subject: Re: Oracle CRS and Split Brin
>
> That is what I mean Kevin, how does a node know which one will be evicted.
>
> For instance if node 1 (the lower node) loses its interconnect what
> happens? The other(s) will be evicted? What happens if the evicted node(s)
> is back to business. Because it cannot contact node 1 through network what
> will happen? (node 1 lost private network)
>
> How does Voting Disk help to determine Split Brain?
>
> Thanks
>
> Alex
>
>
> On 3/28/07, Kevin Closson <kevinc_at_polyserve.com> wrote:
> >
> >
> >
> >
> >
> > When the master node looses its private network, the surviving node
> > becomes the master, reconfiguration of the cluster takes place - the old
> > master is ejected from the cluster configuration - and rebooted. The
> > following can be seen in its crsd.log file (this is for the crs
> > component of the oracle clusterware, responsible for managing oracle
> > resources):
> > .
> > *I AM THE NEW OCR MASTER at incar 6. Node Number = 1 *
> >
> > ..[…lots good CRS stuff deleted…]
> >
> > …This was a very good follow up, but the question was about split brain.
> > Split brain is when there is an equal number of "survivors" and both "think"
> > they are the sole survivor. I think the original post was asking how Oracle
> > determines who gets to anoint themselves the new master in a split brain
> > scenario. I have not seen the full algorithm Oracle uses documented anywhere
> > on the net so if someone has, please let us know. There are a lot of cluster
> > implementations out there. One common approach is to maintain knowledge of
> > the IP addresses of members and use the lowest IP node as one of the factors
> > in choosing the winner in a SB scenario. That is not how CRS does it though
> > as has become evident in a thread I've had with a reader of my blog. In his
> > 2 node case his CRS master was also the lowest IP and in a meltdown
> > scenario, the other node was chosen as the sole survivor. That really
> > surprised me.
> >
> > I think all I've said is Oracle is not telling us what the full
> > algorithm is for survivorship in a true split-brain scenario.
> >
> > There are some clusterware topics here:
> > http://kevinclosson.wordpress.com/kevin-closson-index/real-application-clusters-related-topics/
> >
> > Such as
> > http://kevinclosson.wordpress.com/2007/01/10/comparing-10201-and-10203-linux-rac-fencing-also-fencing-failures-split-brain/
> >
> >
> >
> >
> >
>
>
>
>
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