RAID1 /dev/md4 lost one disk partion /dev/sdb4 after reboot, WHY??

[Bruno Wolff III]

On Sun, Mar 29, 2009 at 20:15:53 +1100,
  L <yuanlux at gmail.com> wrote:
> 
> this partition is about 455GB, there is no IO error from log.

I would suggest looking through /var/log/messages to see if you see any
references to the array or partition and check if any of them shed some
light on what is going on.

It's possible there could be a bug of some sort as well.

For example mdadm has got some issues in rawhide right now. Though I am
not aware of any problems in F9 or F10.