Increasing MAXPHYS

Ulrich Spörlein uqs at spoerlein.net
Sun Mar 21 16:30:54 UTC 2010


On Sat, 20.03.2010 at 12:17:33 -0600, Scott Long wrote:
> Windows has a MAXPHYS equivalent of 1M.  Linux has an equivalent of an
> odd number less than 512k.  For the purpose of benchmarking against these
> OS's, having comparable capabilities is essential; Linux easily beats FreeBSD
> in the silly-i/o-test because of the MAXPHYS difference (though FreeBSD typically
> stomps linux in real I/O because of vastly better latency and caching algorithms).
> I'm fine with raising MAXPHYS in production once the problems are addressed.

Hi Scott,

while I'm sure that most of the FreeBSD admins are aware of "silly"
benchmarks where Linux I/O seems to dwarf FreeBSD, do you have some
pointers regarding your statement that FreeBSD triumphs for real-world
I/O loads? Can this be simulated using iozone, bonnie, etc? More
importantly, is there a way to do this file system independently?

Regards,
Uli


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