machine lockup, witness etc

So i have a machine, 2x 2.8GHz xeon _at_ 533FSB, 4GB of ram,
Adaptec 2120s ASR raid with a 6-disk raid 5. The machine
only runs postgresql.

I find that it just locks up sometimes. I can't get into
the debugger on the serial or the pccons when this happens
(and i can when its normal). I end up power cycling it.

This will often happen if i try to vacuum 2 databases at the
same times for example.

I cvs'upd to head this morning, and the same behaviour
is there (it was 5.2.1).

I've enabled WITNESS, INVARIANTS, INVARIANT_SUPPORT.

Now the machine won't boot, it gets stuck in isa_probe_children()
etc as below.

Any suggestions? I've let it sit here for 15minutes, so i
don't think its just slow. This is from the serial console
and the keystroke to enter it.

db> t
siointr1(c87d9800,c0776340,0,c06d86aa,69e) at siointr1+0xd0
siointr(c87d9800) at siointr+0x21
intr_execute_handlers(c5613c8c,c0c21804,4,c0c21848,c065fe73) at
intr_execute_handlers+0xb1
lapic_handle_intr(34) at lapic_handle_intr+0x3a
Xapic_isr1() at Xapic_isr1+0x33
--- interrupt, eip = 0xc0540f69, esp = 0xc0c21848, ebp = 0xc0c21848 ---
critical_exit(c0736a74,c0c21894,c055c22a,c0741ce0,0) at critical_exit+0x49
_mtx_unlock_spin_flags(c0741ce0,0,c06c4d73,2e2,3) at
_mtx_unlock_spin_flags+0x9d
witness_checkorder(c8767100,9,c06c3f59,c5) at witness_checkorder+0x54a
_mtx_lock_flags(c8767100,0,c06c3f59,c5,ffffffff) at _mtx_lock_flags+0x67
rman_reserve_resource_bound(c078d220,83657eb,82657ea,fff00000,0) at
rman_reserve_resource_bound+0x73
rman_reserve_resource(c078d220,83657eb,82657ea,fff00000,0) at
rman_reserve_resource+0x1c
nexus_alloc_resource(c870c280,c87ce280,3,c0c21c48,83657eb,82657ea,fff00000,0
) at nexus_alloc_resource+0xcb
resource_list_alloc(c87cc440,c870c000,c87ce280,3,c0c21c48) at
resource_list_alloc+0xac
legacy_alloc_resource(c870c000,c87ce280,3,c0c21c48,83657eb,82657ea,fff00000,
0) at legacy_alloc_resource+0x29
bus_generic_alloc_resource(c86e2e80,c87ce280,3,c0c21c48,83657eb,82657ea,fff0
0000,0) at bus_generic_alloc_resource+0x7a
resource_list_alloc(c87cc444,c86e2e00,c87ce280,3,c0c21c48) at
resource_list_alloc+0xac
pci_alloc_resource(c86e2e00,c87ce280,3,c0c21c48,83657eb,82657ea,fff00000,0)
at pci_alloc_resource+0x1a4
bus_generic_alloc_resource(c870dd80,c87ce280,3,c0c21c48,83657eb,82657ea,fff0
0000,0) at bus_generic_alloc_resource+0x7a
resource_list_alloc(c87cc440,c8795b80,c87ce280,3,c0c21c48) at
resource_list_alloc+0x188
isa_alloc_resource(c8795b80,c87ce280,3,c0c21c48,0,ffffffff,1,0) at
isa_alloc_resource+0xca
bus_alloc_resource(c87ce280,3,c0c21c48,0,ffffffff,1,0) at
bus_alloc_resource+0x81
isa_find_memory(c87ce280,c878e80c,c8801800) at isa_find_memory+0x174
isa_assign_resources(c87ce280) at isa_assign_resources+0x88
isa_probe_children(c8795b80) at isa_probe_children+0x14d
configure(0,c1ec00,c1e000,0,c0435b05) at configure+0x32
mi_startup() at mi_startup+0x96
begin() at begin+0x2c
db>