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Re: SATA drives performance

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: SATA drives performance
Date: 2009-12-24 17:05:42
Message-ID: 4B339F66.7020808@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-performance
Mark Mielke wrote:
> Can you be more specific? I am using ext4 without problems than I have 
> discerned - but mostly for smaller databases (~10 databases, one 
> almost about 1 Gbyte, most under 500 Mbytes).

Every time I do hear about ext4, so far it's always in the context of 
something that doesn't work well--not hearing about improvements yet.  
For example, there was a thread on this list earlier this month titled 
"8.4.1 ubuntu karmic slow createdb" that had a number of people chime 
saying they weren't happy with ext4 for various reasons.

Also, I have zero faith in the ability of the Linux kernel development 
process to produce stable code anymore, they're just messing with too 
many things every single day.  Any major new features that come out of 
there I assume need a year or two to stabilize before I'll put a 
production server on them and feel safe, because that this point a 
"stable release" means nothing in terms of kernel QA.  Something major 
like a filesystem introduction would be closer to the two year estimate 
side.  We're not even remotely close to stable yet with ext4 when stuff 
like http://bugzilla.kernel.org/show_bug.cgi?id=14354 is still going 
on.  My rough estimate is that ext4 becomes usable and free of major 
bugs in late 2010, best case.  At this point anyone who deploys it is 
still playing with fire.

> File systems failures have been pretty rare for me lately, so it's 
> hard to say for sure whether my setup is really running well until it 
> does fail one day and I find out.

All of the ext4 issues I've heard of that worry me are either a) 
performance related and due to the barrier code not doing what was 
expected, or b) crash related.  No number of anecdotal "it works for me" 
reports can make up for those classes of issue because you will only see 
both under very specific circumstances.  I'm glad you have a good backup 
plan though.

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


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