Question about nmbclusters

[Konrad Neuwirth <konrad%mailathome.or.at@localhost>]

Hello everyone, 

we are currently facing severe problems with nmbclusters on a NetBSD 6.0 
generic system (amd64). We're running short of nmbclusters, and I do not 
understand how I can increase them. 

sysctl kern.mbuf.nmbclusters
kern.mbuf.nmbclusters = 16384

I see that this number is both derived at boot time (writing another value into 
the kernel has no effect), but I also cannot turn that knob. The only value 
that doesn't lead to an 'invalid argument' error is 16384. I have no idea what 
a better value is, but we've outages of up to ten minutes that take down all 
network interfaces on that system (and we're at six networking interfaces, one 
with three vlans -- and they're mostly well-used). 

So: What can I do to get that value up, to make the system more stable? 

Thank you,
Konrad