'Mount' Considered Harmful to Promise RAID?

[Jud]

The good news:

The problem I'd reported with the installer a week or so ago was corrected  
by the 6-22 version.  DragonFly installed nicely on my third hard drive.

The bad news:

I have an ASUS A7V333 motherboard with a Promise 20276 onboard chip  
controlling two 40-gig IBM 120GXP ATA-100 drives in a RAID0 array.   
Attempting to mount the Win2K slice that is on the array breaks the array:

jud# atacontrol status ar0
ar0: ATA RAID0 subdisks ad4 ad6 status: READY
jud# mount_ntfs /dev/ar0s1 /mnt
mount_ntfs: /dev/ar0s1: Input/output error
jud# atacontrol status ar0
ar0: ATA RAID0 subdisks: ad4 ad6 status: BROKEN
If I don't try to mount the array, it runs perfectly well, as it has for  
years.

Known problem, ideas, ways I can help track down the cause?

Jud