You don't note the process that you used to add the new drive. But my suspicion is that you may not have mounted it. And perhaps if you have, it's not part of the root filesystem.

When you say that it stalls at 10%, that sounds to me suspiciously like it's running out of room... FWIW you can check the free space of your root volume like this:

df -h

On a local TKLDev VM I have running I get this:

Filesystem                Size  Used Avail Use% Mounted on
udev                      2.0G     0  2.0G   0% /dev
tmpfs                     396M   13M  383M   4% /run
/dev/mapper/turnkey-root   25G   21G  2.7G  89% /
tmpfs                     2.0G     0  2.0G   0% /dev/shm
tmpfs                     5.0M     0  5.0M   0% /run/lock
tmpfs                     2.0G     0  2.0G   0% /sys/fs/cgroup
tmpfs                     2.0G     0  2.0G   0% /tmp
/dev/sdb1                  76G   13G   59G  18% /mnt

If you look at the line that is "Mounted on": "/" (i.e. the root volume) you can see that the filesystem is /dev/mapper/turnkey-root (it's an LVM volume) and it's nearly full! Out of interest, I also have a "normal" partition" ("/dev/sdb1") mounted on /mnt.

There's a really old blog post on extending a root volume (with LVM) that Liraz wrote. Whilst it's about 9 years old, the explanation of LVM is still relevant and the commands noted there should also work (assuming you have LVM).

If you don't have LVM, or you hit any issues, please feel free to post back.