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[Xen-users] bidirectional Remus/DRBD HA

I plan on replacing an older Debian based Xen set-up in the next few months.

I am considering also using this as an opportunity to try setting up a two 
machine Remus/DRBD failover/HA system.

To save on hardware costs, I'm wondering if I can distribute the domU guests 
across both machines, where some are
primary on Machine A (secondary on Machine B) and others are primary on Machine 
B (secondary on Machine A).  In
other words, rather than spend on two identical machines where each one targets 
maximum use and Machine B is mostly
not being used, have both machines running as primaries where specific guests 
are primary on each one (and secondary
on the other). So, if I target a need that profiles to 8 cores, use two 4-core 
machines instead of two 8-core machines.
If one machine goes down, then the load temporarily goes up on the lone primary 
but I can live with that (and maybe
use two 6-core machines to offset that in my example).

To keep it simple, I'm thinking two separate DRBD volumes (two physical disks) 
on each machine: One the host machine's
primary, the second one the other machine's secondary.

I realize there are some complexities to keep straight here. Mostly I want to 
know if it's possible (and relatively

A second alternative would be to have the secondary be a lower (and different) 
hardware tier.   But I suspect I'll
have other issues there trying to have things failover to different hardware.

Steve Sapovits

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