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[Discuss] Redundant array of inexpensive servers: clustering?

Kent Borg wrote:
> There is a non-free DRBD that handles more than two nodes. There might
> be something useful down that path.

The point of a quorum disk is the race condition. When the cluster 
splits the nodes race to fence the quorum disk and write their 
signatures. Fencing ensures that only one node can write to the quorum 
disk and the signature identifies the winner to the other nodes in the 
cluster. DRBD on its own can't do this. Corosync + Pacemaker supposedly 
can do it on top of DRBD but that's a full-on HA cluster suite with all 
of the overhead and maintenance that entails.

If you're just doing hot to cold replication with manual switch then you 
don't need a heartbeat or quorum. Just let your hot node do its work, 
let DRBD replicate blocks to the cold node, and if the hot node fails 
then shut it down and flip whatever switch turns the cold node into the 
hot node. Just be sure to do your backups because DRBD will happily 
replicate trashed data to the cold node.

Rich P.

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