[Linux-cluster] Virtual ips 'drifting' from one node toanother

[Rick Stevens]

On Tue, 2007-10-16 at 11:41 -0600, Josh Gray wrote:
> Sorry I'm quite the question asker on the list this week, trying to digest
> the cluster docs pretty quick!
> 
> One more Q - Reading the FAQ section on power fencing.  What is the best
> design for a two (or three) node cluster with dual power supplies?  I would
> assume best with regards to redundancy would be two power switches - one for
> each power supply.  But in the case of fencing shoot outs, should they all
> be on the same single switch?  Am I just over thinking this?

In our configs, we use 8-port APC power strips.  On any given machine,
each power supply is on a separate switch.  Also note that the switches
are on separate circuits as well--the idea being that losing a power
circuit doesn't take a server off-line.

Ordinarily, a machine that uses 2 amps of power will draw 1 amp from
each supply.  However, if you lose a circuit, ALL of the power that
machine is using will come from the remaining supply (2 amps) and will
thus load the power strip twice as heavily.  Make sure you compute the
load of each server and only plug in as many machines as the strip can
handle.  In the above scenario, you obviously can't plug 8 machines into
the strip because if all 8 machines end up drawing 2 amps, that'll
exceed the 15 amp rating of the strip (and possibly the circuit it's
plugged into.

> " same network path as the path used by CMAN for cluster communication"
> Does that mean literally the same ethernet switch or logical vlan, or what?

Technically, the VLAN, but if possible, I'd use the same switch.  One
less thing to poop out.

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- Rick Stevens, Principal Engineer             rstevens at internap.com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
-                                                                    -
-        Hard work has a future payoff. Laziness pays off now.       -
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