Re: Is Diskeeper Automatic Mode safe? - Mailing list pgsql-performance

From Greg Smith
Subject Re: Is Diskeeper Automatic Mode safe?
Date
Msg-id 4B01B3FC.3050405@2ndquadrant.com
Whole thread Raw
In response to Re: Is Diskeeper Automatic Mode safe?  (Robert Schnabel <schnabelr@missouri.edu>)
Responses Re: Is Diskeeper Automatic Mode safe?  (Karl Denninger <karl@denninger.net>)
Re: Is Diskeeper Automatic Mode safe?  (John Rouillard <rouilj@renesys.com>)
List pgsql-performance
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@2ndQuadrant.com  www.2ndQuadrant.com

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