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Comment by trollied | Hacker News Reader

The article is talking about Oracle RAC, and the "crossover" he is talking about was usually really quick Infiniband, not a crossover cable (so, a separate NIC for good reason!). The person that wrote the article doesn't seem to understand RAC enough to actually comment properly. A properly tuned RAC instance will scale horizontally very very well.

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Former (recovering?) Exadata user here. I'll go as far as to say that configuring a best-practices RAC cluster is easier than configuring a best-practices MySQL cluster. RAC solves some additional problems, like discovery and load balancing, that MySQL kicks out to the user (e.g. you have to manage DNS and run a tool like ProxySQL separately).

If you look back far enough, it wasn’t infiniband but a small separate fibrechannel fabric, and further back again I recall buying specialist dual-ported SCSI drives that were marketed primarily for cluster i.e. quorum-disk purposes. More than one goat was required to make these configurations work.

(I seem to recall that many SAS drives now are dual-ported but designed as such to fulfil a desire for multi-path resiliency within storage arrays; this may have different characteristics to those needed of a quorum device)

I’ve seen Oracle RAC in use in many banks in particular where uptime and resilience are critical requirements. It scales well horizontally, but at a very high cost.

How much redundancy do you really have if both (or all N) systems are within 10km of each other?

Alternatively a private L2 network for a N > 2 RAC cluster.

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