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List:       pgsql-performance
Subject:    Re: [PERFORM] DRBD and Postgres: how to improve the perfomance?
From:       Stefan Kaltenbrunner <stefan () kaltenbrunner ! cc>
Date:       2007-09-08 17:25:24
Message-ID: 46E2DB04.1080803 () kaltenbrunner ! cc
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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

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