FC3 with raid1 freeze!!!!

[Dmitry]

Linux hostname.lan 2.6.9-1.681_FC3 #1 Thu Nov 18 15:10:10 EST 2004 i686 i686 i386 GNU/Linux
CPU: Intel(R) Pentium(R) 4 CPU 1.80GHz stepping 02
Motherboard: P4B533-E
Onboard Promise controller - disabled!
Installed: PCI Promis SATA 150 TX2Plus.
2 HDD SATA Maxtor DiamondMax 10 200G

After updating:
kernel-2.6.9-1.681_FC3
kernel-utils-2.4-13.1.39
mdadm-1.6.0-2

# This file is edited by fstab-sync - see 'man fstab-sync' for details
/dev/md0                /                       ext3    defaults        1 1
none                    /dev/pts                devpts  gid=5,mode=620  0 0
none                    /dev/shm                tmpfs   defaults        0 0
none                    /proc                   proc    defaults        0 0
none                    /sys                    sysfs   defaults        0 0
/dev/vg0/usr            /usr                    ext3    defaults        1 2
/dev/vg0/usr_cvsroot    /usr/cvsroot            ext3    defaults        1 2
/dev/vg0/var            /var                    ext3    defaults        1 2
/dev/vg0/swap           swap                    swap    defaults        0 0
/dev/hdb                /media/cdrom            auto    pamconsole,exec,noauto,managed 0 0
/dev/fd0                /media/floppy           auto    pamconsole,exec,noauto,managed 0 0

# mdadm.conf written out by anaconda
DEVICE partitions
MAILADDR root
ARRAY /dev/md1 super-minor=1
ARRAY /dev/md0 super-minor=0

md0 - raid1 for / (ext3)
md1 - raid1 for lvm (see fstab)

When system is running I power off second HDD (/dev/sdb) and my system almost freeze!!! After that I power down my system, plug on power to second HDD and system start. There are no error messages in /var/log/messages about failing /dev/sdb, no error mail from mdadm!

[root at cvs ~]# cat /proc/mdstat 
Personalities : [raid1] 
md1 : active raid1 sdb2[1] sda2[0]
      198113472 blocks [2/2] [UU]
      
md0 : active raid1 sdb1[1] sda1[0]
      1020032 blocks [2/2] [UU]
      
unused devices: <none>

Three months ago I tested FC2 with 2 ATA HDD, and when I powered off
second HDD, system was fine, I got message from mdadm about failing
HDD and my system was still fine.

But FC3 almost freeze. System normally boots from sdb when sda unplugged.

Can someone help me?