During heavy disk I/O (rebuildig raid parity on an 1TB RAID5 spread over 8 SCSI disks) I got the following message, several times per minute:

ahd1: ahd_timeout
ahd1: Timedout SCB already complete. Interrupts may not be functioning.

The server is base on a Tyan 2882D, running 4.0 beta 2 and the boot dmesg is:

Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 4.0_BETA2 (WAP05-Server) #0: Fri Feb 23 14:24:05 CET 2007
	root@weser.math.uni-bonn.de:/var/tmp/obj-4.0beta2/sys/arch/amd64/compile/wap05serv
total memory = 4031 MB
avail memory = 3882 MB
timecounter: Timecounters tick every 10.000 msec
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
mainbus0 (root)
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: AMD Opteron(tm) Processor 246, 1992.45 MHz
cpu0: features: e7dbfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>
cpu0: features: e7dbfbff<PGE,MCA,CMOV,PAT,PSE36,MPC,NOX,MMXX,MMX>
cpu0: features: e7dbfbff<FXSR,SSE,SSE2,LONG,3DNOW2,3DNOW>
cpu0: I-cache 64 KB 64B/line 2-way, D-cache 64 KB 64B/line 2-way
cpu0: L2 cache 1 MB 64B/line 16-way
cpu0: ITLB 32 4 KB entries fully associative, 8 4 MB entries fully associative
cpu0: DTLB 32 4 KB entries fully associative, 8 4 MB entries fully associative
cpu0: AMD Power Management features: f<TTP,VID,FID,TS>
cpu0: AMD Cool`n'Quiet Technology 2000 MHz
cpu0: available frequencies (Mhz): 1000 1800 2000
cpu0: calibrating local timer
cpu0: apic clock running at 199 MHz
cpu0: 16 page colors
ioapic0 at mainbus0 apid 1 (I/O APIC)
ioapic0: pa 0xfec00000, version 11, 24 pins
ioapic1 at mainbus0 apid 2 (I/O APIC)
ioapic1: pa 0xfebff000, version 11, 4 pins
ioapic2 at mainbus0 apid 3 (I/O APIC)
ioapic2: pa 0xfebfe000, version 11, 4 pins
acpi0 at mainbus0: Advanced Configuration and Power Interface
acpi0: using Intel ACPI CA subsystem version 20060217
acpi0: X/RSDT: OemId <A M I ,OEMRSDT ,10000611>, AslId <MSFT,00000097>
acpi0: SCI interrupting at int 9
acpi0: fixed-feature power button present
timecounter: Timecounter "ACPI-Fast" frequency 3579545 Hz quality 1000
ACPI-Fast 24-bit timer
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
PNP0A03 [PCI/PCI-X Host Bridge] at acpi0 not configured
PNP0000 [AT Interrupt Controller] at acpi0 not configured
PNP0200 [AT DMA Controller] at acpi0 not configured
attimer0 at acpi0 (PNP0100): AT Timer
attimer0: io 0x40-0x43
PNP0B00 [AT Real-Time Clock] at acpi0 not configured
pckbc0 at acpi0 (PNP0303): kbd port
pckbc0: io 0x60,0x64 irq 1
pckbc1 at acpi0 (PNP0F03): aux port
pckbc1: irq 12
pcppi0 at acpi0 (PNP0800)
pcppi0: io 0x61
spkr0 at pcppi0
sysbeep0 at pcppi0
PNP0C04 [Math Coprocessor] at acpi0 not configured
com0 at acpi0 (PNP0501-1)
com0: io 0x3f8-0x3ff irq 4
com0: ns16550a, working fifo
com1 at acpi0 (PNP0501-2)
com1: io 0x2f8-0x2ff irq 3
com1: ns16550a, working fifo
PNP0700 [PC standard floppy disk controller] at acpi0 not configured
PNP0C02 [Plug and Play motherboard register resources] at acpi0 not configured
PNP0C02 [Plug and Play motherboard register resources] at acpi0 not configured
PNP0103 [HPET Timer] at acpi0 not configured
PNP0C02 [Plug and Play motherboard register resources] at acpi0 not configured
PNP0C01 [System Board] at acpi0 not configured
acpibut0 at acpi0 (PNP0C0C-170): ACPI Power Button
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard
pcppi0: attached to attimer0
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
ppb0 at pci0 dev 6 function 0: Advanced Micro Devices AMD8111 I/O Hub (rev. 0x07)
pci1 at ppb0 bus 3
pci1: i/o space, memory space enabled
ohci0 at pci1 dev 0 function 0: Advanced Micro Devices AMD8111 USB Host Controller (rev. 0x0b)
ohci0: interrupting at ioapic0 pin 19 (irq 9)
ohci0: OHCI version 1.0, legacy support
usb0 at ohci0: USB revision 1.0
uhub0 at usb0
uhub0: Advanced Micro OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 3 ports with 3 removable, self powered
ohci1 at pci1 dev 0 function 1: Advanced Micro Devices AMD8111 USB Host Controller (rev. 0x0b)
ohci1: interrupting at ioapic0 pin 19 (irq 9)
ohci1: OHCI version 1.0, legacy support
usb1 at ohci1: USB revision 1.0
uhub1 at usb1
uhub1: Advanced Micro OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub1: 3 ports with 3 removable, self powered
vga0 at pci1 dev 6 function 0: ATI Technologies Rage XL (rev. 0x27)
wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100 emulation), using wskbd0
wsmux1: connecting to wsdisplay0
fxp0 at pci1 dev 8 function 0: i82550 Ethernet, rev 16
fxp0: interrupting at ioapic0 pin 18 (irq 11)
fxp0: Ethernet address 00:e0:81:40:a6:00
inphy0 at fxp0 phy 1: i82555 10/100 media interface, rev. 4
inphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
pcib0 at pci0 dev 7 function 0
pcib0: Advanced Micro Devices AMD8111 LPC Controller (rev. 0x05)
viaide0 at pci0 dev 7 function 1
viaide0: Advanced Micro Devices AMD8111 IDE Controller (rev. 0x03)
viaide0: bus-master DMA support present
viaide0: primary channel configured to compatibility mode
viaide0: primary channel interrupting at ioapic0 pin 14 (irq 14)
atabus0 at viaide0 channel 0
viaide0: secondary channel configured to compatibility mode
viaide0: secondary channel interrupting at ioapic0 pin 15 (irq 15)
atabus1 at viaide0 channel 1
Advanced Micro Devices AMD8111 SMBus Controller (SMBus serial bus, revision 0x02) at pci0 dev 7 function 2 not configured
amdpm0 at pci0 dev 7 function 3: Advanced Micro Devices AMD8111 ACPI Controller (rev. 0x05)
timecounter: Timecounter "amdpm0" frequency 3579545 Hz quality 1000
amdpm0 24-bit timer
iic0 at amdpm0: I2C bus
adt7463c0 at iic0 addr 0x2e
amdpm0: random number generator enabled (apprx. 57ms)
ppb1 at pci0 dev 10 function 0: Advanced Micro Devices AMD8131 PCI-X Tunnel (rev. 0x12)
pci2 at ppb1 bus 2
pci2: i/o space, memory space enabled
ahd0 at pci2 dev 6 function 0
ahd0: Enabling 39Bit Addressing
ahd0: interrupting at ioapic1 pin 0 (irq 5)
ahd0: aic7902: Ultra320 Wide Channel A, SCSI Id=7, PCI-X 67-100 MHz, 512 SCBs
scsibus0 at ahd0: 16 targets, 8 luns per target
ahd1 at pci2 dev 6 function 1
ahd1: Enabling 39Bit Addressing
ahd1: interrupting at ioapic1 pin 1 (irq 10)
ahd1: aic7902: Ultra320 Wide Channel B, SCSI Id=7, PCI-X 67-100 MHz, 512 SCBs
scsibus1 at ahd1: 16 targets, 8 luns per target
bge0 at pci2 dev 9 function 0: Broadcom BCM5704C Dual Gigabit Ethernet
bge0: interrupting at ioapic1 pin 0 (irq 5)
bge0: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:40:a6:18
brgphy0 at bge0 phy 1: BCM5704 1000BASE-T media interface, rev. 0
brgphy0: using BCM5704 DSP patch
brgphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
bge1 at pci2 dev 9 function 1: Broadcom BCM5704C Dual Gigabit Ethernet
bge1: interrupting at ioapic1 pin 1 (irq 10)
bge1: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:40:a6:19
brgphy1 at bge1 phy 1: BCM5704 1000BASE-T media interface, rev. 0
brgphy1: using BCM5704 DSP patch
brgphy1: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
aapic0 at pci0 dev 10 function 1: Advanced Micro Devices AMD8131 IO Apic (rev. 0x01)
ppb2 at pci0 dev 11 function 0: Advanced Micro Devices AMD8131 PCI-X Tunnel (rev. 0x12)
pci3 at ppb2 bus 1
pci3: memory space enabled
aapic1 at pci0 dev 11 function 1: Advanced Micro Devices AMD8131 IO Apic (rev. 0x01)
pchb0 at pci0 dev 24 function 0
pchb0: Advanced Micro Devices AMD64 HyperTransport configuration (rev. 0x00)
pchb1 at pci0 dev 24 function 1
pchb1: Advanced Micro Devices AMD64 Address Map configuration (rev. 0x00)
pchb2 at pci0 dev 24 function 2
pchb2: Advanced Micro Devices AMD64 DRAM configuration (rev. 0x00)
pchb3 at pci0 dev 24 function 3
pchb3: Advanced Micro Devices AMD64 Miscellaneous configuration (rev. 0x00)
isa0 at pcib0
lm0 at isa0 port 0x290-0x297: W83627HF
ioapic0: enabling
ioapic1: enabling
ioapic2: enabling
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
Kernelized RAIDframe activated
IPsec: Initialized Security Association Processing.
atapibus0 at atabus0: 2 targets
scsibus0: waiting 2 seconds for devices to settle...
scsibus1: waiting 2 seconds for devices to settle...
cd0 at atapibus0 drive 0: <SONY DVD-ROM DDU1615, , FYS2> cdrom removable
cd0: 32-bit data port
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33)
cd0(viaide0:0:0): using PIO mode 4, Ultra-DMA mode 2 (Ultra/33) (using DMA)
ugen0 at uhub1 port 1
ugen0: Phoenixtec Power USB Cable (V2.00), rev 1.00/0.06, addr 2
sd0 at scsibus0 target 0 lun 0: <FUJITSU, MAX3036NC, 0104> disk fixed
sd0: 35068 MB, 49158 cyl, 2 head, 730 sec, 512 bytes/sect x 71819496 sectors
sd0: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd1 at scsibus0 target 2 lun 0: <FUJITSU, MAX3036NC, 0104> disk fixed
sd1: 35068 MB, 49158 cyl, 2 head, 730 sec, 512 bytes/sect x 71819496 sectors
sd1: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
ugen1 at uhub1 port 2
ugen1: Phoenixtec Power USB Cable (V2.00), rev 1.00/0.06, addr 3
sd2 at scsibus1 target 0 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd2: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd2: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd3 at scsibus1 target 1 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd3: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd3: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd4 at scsibus1 target 2 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd4: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd4: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd5 at scsibus1 target 3 lun 0: <FUJITSU, MAT3147NC, 0109> disk fixed
sd5: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd5: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd6 at scsibus1 target 4 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd6: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd6: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd7 at scsibus1 target 5 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd7: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd7: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd8 at scsibus1 target 6 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd8: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd8: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
sd9 at scsibus1 target 8 lun 0: <FUJITSU, MAW3147NC, 0104> disk fixed
sd9: 136 GB, 78753 cyl, 5 head, 729 sec, 512 bytes/sect x 287277984 sectors
sd9: sync (6.25ns offset 127), 16-bit (320.000MB/s) transfers, tagged queueing
raid1: RAID Level 1
raid1: Components: /dev/sd0e /dev/sd1e
raid1: Total Sectors: 35909632 (17534 MB)
raid0: RAID Level 0
raid0: Components: /dev/sd0f /dev/sd1f
raid0: Total Sectors: 71819264 (35068 MB)
boot device: raid1
root on raid1a dumps on raid1b
root file system type: ffs