'Root is full' problem

[R Kimber]

I'm getting 'root is full' messages after installing a new USB drive, but I
can't work out how to sort it out.

The background is:-

I had a failing USB drive (there are two).
I unmounted both USB drives.
I commented out both drives in /etc/fstab.
I unplugged the failing drive.
I rebooted.

I used gparted to format the new drive.

It turned out that the good USB drive was mounted after the reboot, though
not of course the new drive, but not where it had been specified in fstab.
(How does that happen? I thought fstab controlled drive mounting). And I
get the 'root is full' message.

So, where do I go from here?

And how do I specify where USB drives are mounted (scripts are involved so
I need to know where they are).  I thought I could mount drives wherever I
wanted.

Thanks,

- Richard.

-- 
Richard Kimber