System freezes on Blade 100/150 - possible due to file buffers

[Connor McLaughlan <cont6pro3%gmail.com@localhost>]

Hello All,

for a while now i am experiencing system freezes on a Blade 100 and a
Blade 150 with NetBSDs from 9.0-9.3, seemingly related to files
transfered to harddisk.
If i don't copy anything to the harddisk from usb or network, the
systems stay up forever.

I tried to build all kinds of different kernels, falling back to
generic controller drivers or disabling dma and udma. Nothing helped
so far. I don't get any error, the systems just freeze.

I suspect an issue with the buffer cache:
I am experiencing the freezes also when i run the systems from a
NetBSD install CD. However i found out, that if i keep the file buffer
(as given by top - xxM File) below 800mb the systems will stay up and
running.

I only found a single method to evict the buffer caches - by
unmounting and remounting the source and target drives, which seems to
only be possible using a boot CD, as i found no option to remount a
drive on a running system (is this possible in NetBSD, like in linux:
mount -o remount,rw ...?)

Also i tried to modify a few of the vm.* subtree values like
vm.bufcache and vm.bufmem_hiwater via sysctl to see if this has any
effect on the buffer cache evicting files or not growing too large,
without success.

Is there a command to release all the buffer caches or a possibility
to disable caching? (I commented out both buffer strategies
BUFQ_READPRIO and BUFQ_PRIOSCAN and also tried to set bufcache to 0
and built a new kernel, which did not disable the file buffering.

Does anyone have any ideas about this behavior or experienced it also?

Regards,
Connor