[Linux-cluster] Quorum disk over RAID software device

[Rafael Micó Miranda]

Hi Brem

El mar, 15-12-2009 a las 17:21 +0100, brem belguebli escribió:
> Hi,
> 
> The problem you could encounter is the network and storage split brain.
> 
> If your Qdsik LUNs were hosted by 2 arrays located in 2 different
> rooms or site, each room hosting half the nodes of your cluster, in
> case a SAN and network partition occurs between the 2 rooms, you'll
> find yourself in a perfect storage and network split brain.
> 
> Each room having the same number of nodes and accessing one leg of
> your qdisk, each qdisk leg being seen "alive" by the nodes in the
> room.
> 
> Brem
> 

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I thought about this. In my situation:

- All the nodes are in the same site.
- All the nodes are connected to the two storage arrays via the same FC
switches in a symmetric way. 
- All the nodes have their network interfaces connected to the same
couple of Ethernet Switches in a symmetric way via bonding.

I think the probability of failing exactly the devices that should fail
(5 exact FC ports in one FC switch, another 5 on the another FC switch
and a "split" in the Ethernet switches themselves exactly dividing the
nodes in groups of 3) is pretty small.

I see you exposed your point with the idea of a multi-site cluster with
the 2 qdisk LUNs placed in different sites and cluster nodes in both of
them, but this is not the case. But that is, in fact, a really
interesting scenario :)

Thanks for your interest. Cheers,

Rafael

-- 
Rafael Micó Miranda