virtual box create and add new drive

Find the machine you want with

vboxmanage list vms

I then go to the directory where this VM is location

Create HDD

VBoxManage createhd --filename YUM_Repos.vdi --size 50000

0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%

Medium created. UUID: 813790e1-e351-41dc-8f2e-160baf98d279

Now Attach Drive to Machine

VBoxManage storageattach $VM --storagectl "SATA Controller" --port 0  --device 1 --type hdd --medium $VM.vdi