What's an easy way to replace a drive?

[Anthony Atkielski]

The continuing problems I'm having with my SATA drives seem to center on
only one of the two drives, /dev/ad10, and since both drives are
identical (Western Digital WD1200JD 120-GB SATA drives), this is a good
indicator that the drive itself might be failing.  So I've decided to
spend $83 and buy a replacement drive to see if that fixes the problem.

Now, what's the easiest way to replace the drive?  The drive I want to
replace contains only /var and /tmp.  Are these mounted in single-user
mode?  I was thinking perhaps I can just replace the drive, set up
identical slices on the new drive, then restore /var and /tmp from the
latest backup.  Can I restore from tape in single-user mode?

I don't have any extra connectors to which I can attach this drive
without removing one of the other drives, so I'm looking for a way to
fix it up by just removing the old drive and putting in the new one,
without the need to have both old and new drives online at the same
time.

-- 
Anthony