Hi David,
On Wed, Oct 20, 2021 at 6:23 AM David Cunningham <dcunningham@xxxxxxxxxxxxx> wrote:
Hello,I've a few questions about conflict resolution in a net-split scenario:1. What are the default values for cluster.server-quorum-type and cluster.server-quorum-ratio? (at the moment "gluster volume info gvol0" does not report either)
$gluster volume get gvol0 cluster.server-quorum-type
$gluster volume get all cluster.server-quorum-ratio
2. If there are 3 mirrored nodes and cluster.server-quorum-ratio is 50, and node1 and node2 are net-split from node3, then am I right in thinking that the volume on node3 will automatically shut down and prevent access thus preventing a conflict?
Yes, the glusterd on node 3 will kill the brick processes on that node.
3. If there are 2 mirrored nodes and a net-split happens and cluster.server-quorum-ratio is 50 then:a) If existing file A is changed on node1 and node2 then the file will enter net-split state, right?
Yes, for 2 node setups, you must set the ratio to 51% to avoid this. I'm assuming that the 'changing' that you refer to is happening via fuse mounts on each of these nodes.
b) If existing file B is changed on node1 but not node2 then will the file enter a net-split state?
No.
c) If new file C is written on node1 but not node2 then will the file enter a net-split state?
No.
4. Is the outcome of conflict resolution at a file level the same whether node3 is a full replica or just an arbiter?
server quorum feature is not related to replication. It really is a glusterd thing and doesn't really help prevent split-brains, because split-brains are caused by failed I/Os from clients and the clients can be mounted even outside the storage pool. What you need to ensure is that cluster.quorum-type (which is 'client' quorum) is set to auto for replica 3 and arbiter. It already is by default. See https://docs.gluster.org/en/latest/Administrator-Guide/arbiter-volumes-and-quorum/#split-brains-in-replica-volumes for more info.
-Ravi
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