Kernel won't dump on panic

[Gerald Heinig]

Hi all,

I'm having problems getting a kernel to write a crash dump on my Dell 
Optiplex under FreeBSD 5.3.

I've set dumpdev="/dev/ad0s1b", set kern.sync_on_panic to 1, the dump 
device has enough space (1 Gig, physical RAM is 512M).
When the kernel panics, it starts writing out a vmcore, but only gets to 
2 blocks and then stops.

Things work fine with my dual processor Tyan Tiger box.

Anyone have any ideas as to what I might be doing wrong?

Cheers,
Gerald