Kevin Stevens wrote:
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.
Hmmm ... perhaps I'm wrong. I thought that was it, but I remember more
information about the testing that led to decisions about the way the
filesystem works.
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?
Yes. While I don't understand the deep magic of it, the fact is the amount
of free space needed to ensure efficient block allocation is a percentage
of total filesystem space.
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.
Well, fact is you _can_ fill a disk past the 92% mark. But as a sysadmin,
you'll definately want to be alerted to this because the write algorithm
changes from time to space and performance drops dramatically.
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!
I see where you're coming from. Glad I could help clear it up.
--
Bill Moran
Potential Technologies
http://www.potentialtech.com
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