Soft RAID1 and SATA - Hardware failure test - I power off disk and system freezes

[Jan Stavel <stavel@brailcom.org>]

Hello,
I installed debian 3.1 on server:

vendor_id       : AuthenticAMD
cpu family      : 15
model           : 47
model name      : AMD Athlon(tm) 64 Processor 3500+
stepping        : 2
cpu MHz         : 2199.844

with ViaPro chipset and SATA disks

  VIA Technologies, Inc. VT8237 PCI bridge [K8T800 South]
  Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet (rev 10)
  VIA Technologies, Inc. VIA VT6420 SATA RAID Controller (rev 80)
  Inc. VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE (rev 06)
  VIA Technologies, Inc. VT8237 ISA bridge [K8T800 South]

I switched off raid in Bios and installed Software Raid:

  Personalities : [raid0] [raid1] [raid5]
  md0 : active raid1 sdb1[1] sda1[0]
        497856 blocks [2/2] [UU]

  md2 : active raid1 sda3[0] sdb3[1]
        4417792 blocks [2/2] [UU]

  md1 : active raid1 sdb2[1] sda2[0]
        112302272 blocks [2/2] [UU]

  unused devices: <none>

If I do software failure it works well:

  mdadm /dev/md0 -f /dev/sda1
  mdadm: set /dev/sda1 faulty in /dev/md0

  md0 : active raid1 sdb1[1] sda1[2](F)
        497856 blocks [2/1] [_U]


But if I try to power off a disk (unplug the power cable) the system 
freezes. I cannot read /proc/mdstat. The only way to get the system 
running is to do restart.

Do I do something wrong when trying hardware fauilure?

Thanks,
Jan Stavel