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Re: Questions regarding Galera Cluster


----- On 12 Jun, 2015, at 6:36 PM, Dan Storm storm@xxxxxxxx wrote:

> Hello.
> I just saw this YouTube video: https://www.youtube.com/watch?v=hYSGsgIyshs
> It was really informative and it seems like a simple and easy setup.
> Now, I have a few questions which is regarding maintaining a Galera Cluster,
> which I hope to get some answers on.
> 1. A cluster should have an odd number of nodes to avoid brain split.

Split brain is avoided with 3+ nodes. You won't get split brain with even nodes as the quorum is 1/2 + 1 nodes.
i.e. It does mean 1/2 the nodes can't form a quorum.

> In case I
> hit the wall with insufficient disk space and I need to scale up my servers,
> which steps would be the appropriate? My initial thoughts would be taking down
> one node at a time and add a larger node, what for it to have replicated from
> the other nodes.
> Would the - now even numbered of nodes - handle this?

Bit vague.

Stick to your even (>2) nodes.

> And what will have when I
> do this to the bootstrapped server (the one the others connects to)?

same as any cluster initialisation

> 2. According to the video, a slave replication of the cluster would be a way of
> securing my data in case of disaster. Would creating dumps regularly not
> suffice? And secondly, in case of hardware failure on one of the nodes,
> bringing in a new node (probably asking the same as before) would hopefully
> just replicate the data when it joins again?

Look up the important conceptual difference between backup and DR.

Make sure what you have meets your requirements for doing a restore (related to backup) in a workable time covering the business requirements.
Backup covers things like dumb user did a DELETE without a where clause, SQL injection and general data corruption that will affect all nodes.

The DR recovery mechanism (hardware failure etc... ) covers your calculated business and technical risks.

Hint, you many need more that one mechanism.

Daniel Black, Engineer @ Open Query (http://openquery.com.au)
Remote expertise & maintenance for MySQL/MariaDB server environments.

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