Here is a subject that does not get enough attention. With RHCS/CMAN, the heartbeat of a node, by default, uses broadcast to let the other nodes know that it is alive and well, and is a member of the cluster. So, in turn, by default we are restricted to using a single network for our heartbeat, and in most cases this is fine… But, what if we want to cluster across multiple networks? Say I have node01 on 10.1.1.0/24 and node02 on 10.1.2.0/24, and I want them to be able to communicate with each other? Well, this is not as trivial a feat as you might assume… In fact, I had to employ some of the finest network technicians (well, not really — but they are pretty smart!) in the south-east to get this to work… Continue reading »

… What the? Ok, so the basic idea here is that we’re going to be creating a cluster, sharing a block device from one server to the other nodes in a cluster as a Global Network Block Device, putting it into an LVM configuration, and formatting the filesystem using Global File System for file locking between nodes… And we’re gonna do this all natively with Red Hat Clustering Suite. This is a good, low-rent implementation of block device sharing in a cluster, where iSCSI or FCP is not available to the hosts. It’s better than NFS because we get real locking mechanisms, and we get our own fencing mechanism for the cluster (which, unfortunately I won’t be covering in this post). I’ve recently had the opportunity to do this as a proof of concept and this is really cool stuff… Continue reading »

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