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:
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> 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*
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> ..[…lots good CRS stuff deleted…]
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> …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.
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> 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.
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> There are some clusterware topics here:
> http://kevinclosson.wordpress.com/kevin-closson-index/real-application-clusters-related-topics/
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> 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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