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Date:      Fri, 24 Jan 2003 21:02:21 -0800
From:      Kevin Stevens <Kevin_Stevens@pursued-with.net>
To:        Bill Moran <wmoran@potentialtech.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Filesystem tuning parameters
Message-ID:  <2F48C1C3-3022-11D7-8DC1-003065715DA8@pursued-with.net>
In-Reply-To: <3E31DD12.10601@potentialtech.com>

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On Friday, Jan 24, 2003, at 16:40 US/Pacific, Bill Moran wrote:
> See
> /usr/share/doc/papers/diskperf.ascii.gz
> on your system.  This is the authoritative resource as to why those 
> settings
> are they way they are.

??  Sure that's the correct doc?  It involves throughput tests  of 
different disk systems on VAXen, but doesn't really discuss any of 
these parameter changes.  They do go into rotational delay a bit.

> So ... it's like this:
> 1) If you really want to fill your drive up past 90%, understand that 
> UFS
>    simply isn't designed to do that efficiently.

Ok... and what you're confirming is that this is a percentage 
requirement, so it doesn't vary significantly between 120MB and 120GB 
filesystems?

> 4) If you bought a 120G drive because you have 119.5G of data to 
> store, I
>    think you made a mistake and should either return it for a bigger 
> drive
>    or accept the performance hit.

My confusion came from various bits of documentation that suggest the 
primary purpose of minfree is to provide notification and buffer 
time/space for sysadmins to deal with filesystems nearing capacity.  In 
my scenario, 12GB would be total overkill to commit for that purpose, 
regardless of how much data I needed to store.  Understanding that it 
is required for filesystem overhead makes the resource usage 
justifiable.  Thanks!

KeS


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