Hi everyone!
I need a sanity check on our Server Quorum Ratio settings to ensure the maximum uptime for our virtual machines. I'd like to modify them slightly, but I'm not really interested in experimenting with live servers to see if what I'm doing is going to work, but I think that the theory is sound.
We have a Gluster array of 3 servers containing two Replicate bricks.
Brick 1 is a 1x3 arrangement where this brick is replicated on all three servers. The quorum ratio is set to 51%, so that if any one Gluster server goes down, the brick is still in Read/Write mode and the broken server will update itself when it comes back online. The clients won't notice a thing, while still ensuring that a split-brain condition doesn't occur.
Brick 2 is a 1x2 arrangement where this brick is replicated across only two servers. The quorum ratio is currently also set to 51%, but my understanding is that if one of the servers that hosts this brick goes down, it will go into read-only mode, which would probably be disruptive to the VMs we host on this brick.
My understanding is that since there are three servers in the array, I should be able to set the quorum ratio on Brick2 to 50% and the array will still be able to prevent a split-brain from occurring, because the other two servers will know which one is offline.
The alternative of course, is to simply flesh out Brick2 with a third disk. However, I've heard that 1x2 replication is faster than 1x3, and we'd prefer that extra speed for this task.
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Krist van Besien
senior architect, RHCE, RHCSA Open Stack
Red Hat Red Hat Switzerland S.A.
krist@xxxxxxxxxx M: +41-79-5936260
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