2nd hard drive failed

[Mervyn Passmore]

Hi,
I have Freebsd 4.11 (I think it is 4.11, not really sure how to tell but
definitely 4.x because the SCO emulator on 5.x doesn't work) on a PC with
two hard drives. The second one was installed as a spare in case of
emergency or temporary backups etc but has never been really used. It is now
failing, making odd mechanical sounds and I get messages on the console such
as:

ad3 READ timeout
ata1 Resetting devices

when anything attempts to connect to it, eg /stand/sysinstall

How can I disable it from the system so I can shutdown, remove it and
restart the PC?

The PC also has an obsolete SCSI card I'd like to remove at the same time.
Is this a similar process?

Thanks
Mervyn