One of my inn 1.4unoff4 news reader servers started throttling itself just today with "Interrupted system call writing article file" (happened twice in the past 24 hours). The spool is on an F230 running 4.0.3, 256MB of read cache and 4MB of write cache. The news server is an Ultra 170, 512MB of RAM, ~250 to 300 readers around peak times. The two are on a FDDI ring.
The F230 hovers around 65% CPU usage, so I don't think that's the problem, but the Ultra is reporting 900 to 1200 packets per second both in and out of its FDDI interface. Half of its time is spent in the kernel, according to top(1). The mounts are NFSv3 over UDP. Would dropping back down to NFSv2 help any? I'm trying to determine if this is a network congestion problem, or an OS limitation (on either the Netapp or the Sun).