Message-ID: <46E2DB04.1080803@kaltenbrunner.cc>
Date: Sat, 08 Sep 2007 19:25:24 +0200
From: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
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To: "Joshua D. Drake" <jd@commandprompt.com>
CC: Gregory Stark <stark@enterprisedb.com>,
	Simon Riggs <simon@2ndquadrant.com>,
	Bernd Helmle <mailings@oopsware.de>,  mfatticcioni@mbigroup.it,
	pgsql-performance@postgresql.org
Subject: Re: DRBD and Postgres: how to improve the perfomance?
References: <2C070D1C3970467FF64F6B6A@imhotep.credativ.de>
	<1189232904.4281.19.camel@ebony.site>
	<87k5r1zd52.fsf@oxford.xeocode.com>
	<46E2CAAF.50205@commandprompt.com>
	<46E2CEF3.1030908@kaltenbrunner.cc>
	<46E2D38A.6070607@commandprompt.com>
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Joshua D. Drake wrote:
> Stefan Kaltenbrunner wrote:
>> Joshua D. Drake wrote:
>>> Gregory Stark wrote:
>>>> "Simon Riggs" <simon@2ndquadrant.com> writes:
>>>>> You're right, but the distinction is a small one. What are the chances
>>>>> of losing two independent servers within a few milliseconds of each
>>>>> other? 
>>>> If they're on the same power bus?
>>> That chance is minuscule or at least should be. Of course we are
>>> assuming some level of conditioned power that is independent of the
>>> power bus, e.g; a UPS.
>> how is that making it different in practise ? - if both are on the same
>> UPS they are affectively on the same power bus ...
> 
> Well I was thinking the bus that is in the wall. I would assume that
> people were smart enough to have independent UPS systems for each server.
> 
> city power->line conditioning generator->panel->plug->UPS->server
> 
> wash, rinse repeat.

the typical datacenter version of this is actually more like:

city power->UPS (with generator in parallel)->panel->plug

or

city power->flywheel->(maybe UPS)->panel->plug

it is not really that common to have say two different UPS feeds in your
rack (at least not for normal housing or the average corporate
datacenter) - mostly you get two feeds from different power distribution
panels (so different breakers) but that's about it.
Having a local UPS attached is usually not really that helpful either
because those have limited capacity need space and are an additional
thing that can (and will) fail.


Stefan