Promise Fastrak ATA RAID 1 mirror lost

[Michael]

Hi,

I have an intel motherboard with an onboard Promise Fastrak ATA RAID. 
This morning it reported that the mirror was lost and I would like to 
rebuild it.

My system is FreeBSD 4.8-RELEASE-p10. This is what's reported from 
`atacontrol list`:
ATA channel 0:
     Master: acd0 <CD-540E/1.0A> ATA/ATAPI rev 0
     Slave:       no device present
ATA channel 1:
     Master:      no device present
     Slave:       no device present
ATA channel 2:
     Master:  ad4 <ST380021A/3.19> ATA/ATAPI rev 5
     Slave:       no device present
ATA channel 3:
     Master:  ad6 <ST380021A/3.19> ATA/ATAPI rev 5
     Slave:       no device present

The kernel message that I saw in my daily report was this:
ad6: hard error reading fsbn 140018943 of 0-127 (ad6 bn 140018943; cn 
138907 tn
10 sn 57) trying PIO mode
ad6: DMA problem fallback to PIO mode
ad6: DMA problem fallback to PIO mode
ad6: DMA problem fallback to PIO mode
ad6: DMA problem fallback to PIO mode
ad6: hard error reading fsbn 140019007 of 0-127 (ad6 bn 140019007; cn 
138907 tn
11 sn 58) status=59 error=00
ar0: WARNING - mirror lost

Which is confirmed by the output of `atacontrol status ar0`:
ar0: ATA RAID1 subdisks: ad4 ad6 status: DEGRADED

So I looked at the handbook 
(<http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/raid.html>) 
and in section 12.4.3 it suggests that I detach, attach and then 
rebuild the array. Can I do this on a running system or do I first need 
to drop to single user mode? If I do that, how do that without 
rebooting? Does anyone have any experience with this?

The other option seems to be to reboot the computer and use the Fastrak 
firmware to rebuild the array.

Which option is the most painless? I have recent dumps of the system, 
but I would prefer not to have to go that route.

Thanks for any help/suggestions,

Michael