Very slow system using dd / nfs

Hello guys,

I am testing FreeBSD 6.2 NFS support, using linux-kernel-nfs as server.
Now I am starting two instances of testdisks.sh [0] with forks=500
and directory set to /nfs/teufeli2/ (/nfs = nfs volume, teufeli2 is the
host name). After some minutes the system has about 1500 processes
running (which is pretty ok), but is extremly slow:

- typing characters is delayed for about 10-20 seconds
- typing ctrl+a " in screen takes about 30 seconds to display the menu
- changing virtual consoles is fast (via ctrl+f[n])
- login in is still possible, though sometimes it takes longer than 300
seconds, which leads to a timeout

I am wondering why the system behaves that way and what would be the
correct way to priorize keyboard input for instance?

The problem looks somehow similar to the problems I've seen with gmirror
and our scsi disks (summary at [1]).

Is it possible that freebsd has some quirks when having heavy i/o load
in general?

With heavy i/o load I mean about 500-1000 processes trying to access the
disk system.

I am currently trying to do some performance tests on freebsd to find out

a) whether running a mailserver on a NFS volume would be possible
(for a mailserver cluster)
b) what todo to increase reaction time from a freebsd, so it's still
maintainable under heavy i/o load
c) what todo to increase mail server performance under freebsd in
general?
d) is nfs reliable under freebsd?


Sincerly

Nico

[0]: http://home.schottelius.org/~nico/unix/freebsd/testdisks.sh
[1]: Message-ID: <20070629111626.GF7663@xxxxxxxxxxxxxxx> on freebsd-geom@

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