Moving /opt to new disk

Recently I was playing with a Kali VM and I installed so much stuff to it that I used up the disk!  Literally, I was at 100% used!  Yikes!  

I started to try to delete unnecessary files, trash, cached apt packages, etc, but quickly came to the conclusion that I wanted everything that I had on the Kali VM, and my disk was still 96% full.  So I needed a way to offload files that I still wanted.  

I looked through my VM, which had a single 20GB hard drive, and saw that /usr had 10GB by itself, and /opt had 4GB.  So I decided to create a new virtual hard drive, move over my /opt files, and change /opt's location in /etc/fstab to point to the new directory.   This solved my problem, as my drive that USED to say 96% full, now says 73% full, just by moving /opt.   

Here's how I moved it:

I added a new virtual hard drive in VirtualBox that was 12GB.  

I booted up the VM, went into fdisk, and noted (by doing 'ls /dev/sd*') that my new drive was called sdb.  I used fdisk to create a new primary partition and write the changes.  

I then made a file system on that newly created partition with:

#mkfs -t ext3 /dev/sdb1

Then I went into single user mode to ensure that I could copy over all the /opt files

#init 1

After I booted into single user mode, I did this:

#mkdir /mnt/Disk2opt

#mount /dev/sdb1 /mnt/Disk2opt

#cp -avx /opt/* /mnt/Disk2opt/

#mv /opt /opt_old

#ln -s /mnt/Disk2opt /opt

I then added this line to the /etc/fstab

'/dev/sdb1   /opt   ext3    defaults   1  2'

That was it!   After I rebooted and saw that everything was working fine, I deleted the /opt_old directory, and freed up all that space.  That made my 96% used drive go down to 73% used!   Awesome!