Enable USB storage on LibreCMC router

I have successfully managed to install LibreCMC on a Netgear WNDR3800 router.

I have also successfully installed the necessary software to enable USB.

But I fail to mount the external drive. According to https://wiki.openwrt.org/doc/howto/usb.storage
one should run the following commands:
mkswap /dev/sda1
swapon /dev/sda1
mkdir -p /mnt/share
mount -t ext4 /dev/sda2 /mnt/share -o rw,sync

When I run the last line I am told that the device doesn't exist. Running 'ls' verifies that and I have tried every possible and impossible partition name that I can think of (i.e. sda1, sda2, sdb1, sdb2 etc).

So what am I doing wrong?