Re: Is Diskeeper Automatic Mode safe?

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Robert Schnabel <schnabelr(at)missouri(dot)edu>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, cb <cb(at)mythtech(dot)net>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Is Diskeeper Automatic Mode safe?
Date: 2009-11-16 20:20:12
Message-ID: 4B01B3FC.3050405@2ndquadrant.com
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Robert Schnabel wrote:
> Nope. Forgive my ignorance but isn't that what a UPS is for anyway?
> Along with a BBU controller.
If you have a UPS *and* a BBU controller, then things are much
better--those should have a write cache that insulates you from the
worst of the problems. But just a UPS alone doesn't help you very much:

1) A UPS is built with a consumable (the battery), and they do wear
out. Unless you're proactive about monitoring UPS battery quality and
doing tests, you won't find this out until the first time the power goes
out and the UPS doesn't work anymore.
2) Do you trust that the UPS integration software will *always* shut the
server down before the power goes out? You shouldn't.
3) Ever had someone trip over the cord between the UPS and the server?
How about accidentally unplugging the wrong server? These things
happen; do you want data corruption when they do?
4) There are all sorts of major electrical problems you can run into
(around here it's mainly summer lightening) that will blow out a UPS
without giving an opportunity for graceful shutdown.

If there's anyone who thinks a UPS is all you need to be safe from power
issues, I know a guy named Murphy you should get introduced to.

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com

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