Replacing hard disk used in existing filesystem

[Mark Fletcher <mark@fletcher.net>]

Hello the list!

My Debian (wheezy am464, upgraded from an original squeeze install)
system started complaining yesterday that one of my hard disks is about
to fail. I suspect it suffered damage in the earthquake that recently
hit Japan (I'm in Tokyo) and has been quietly deteriorating since.

Anyway the disk concerned is a 1TB disk on which is mounted /opt, so I
feel I should be able to replace it without major hassle. I have already
backed it up fully to NAS.

The only issue is that I don't have enough spare power connectors on my
PC's power supply to attach both the new and the old disks at the same
time.

What I want to know is how can I remove the current drive from the
filesystem so I can remove it physically without sending the machine
into a tailspin? I have only ever set up the mapping of disk partitions
to mount points at installation time, never afterwards, and so am not
sure what to do.

I am thinking the procedure will be something along the lines of:

1) modify my computer's mount settings such that /opt is part of the
root filesystem instead of a separate mount point (HOW? manual edit
of /etc/fstab or something more sophisticated?) This will cause me to
lose access to everything on the old disk which is OK because it's all
backed up and there is nothing there that's critical to the running of
the machine.

2) Power down the machine and remove the old disk, attach the new disk.

3) bring up the machine, partition and format the new disk. (is the tool
for this fdisk?)

4) modify the machine's mount settings to go back to mounting /opt on
the new disk (HOW?)

5) restore everything I want in /opt back from the backup.

Even assuming I'm on the right lines, I don't know how to do steps 1 and
4 and am not totally confident about how to do 3, so would appreciate
any advice.

Cheers

Mark