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Re: [Linux-cluster] Starter Cluster / GFS

Digimer wrote:
On 10-11-10 07:17 AM, Gordan Bobic wrote:
If you want the FS mounted on all nodes at the same time then all
those nodes must be a part of the cluster, and they have to be
quorate (majority of nodes have to be up). You don't need a quorum
block device, but it can be useful when you have only 2 nodes.
At term, I will have 7 to 10 nodes, but 2 at first for initial setup
and testing. Ok, so if I have a 3 nodes cluster for exemple, I need at
least 2 nodes for the cluster, and thus the gfs, to be up ? I cannot
have a running gfs with only one node ?
In a 2-node cluster, you can have running GFS with just one node up. But
in that case it is advisble to have a quorum block device on the SAN.
With a 3 node cluster, you cannot have quorum with just 1 node, and thus
you cannot have GFS running. It will block until quorum is re-established.

With a quorum disk, you can in fact have one node left and still have
quorum. This is because the quorum drive should have (node-1) votes,
thus always giving the last node 50%+1 even with all other nodes being dead.

I've never tried testing that use-case extensively, but I suspect that it is only safe to do with SAN-side fencing. Otherwise two nodes could lose contact with each other and still both have access to the SAN and thus both be individually quorate.


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