How to mount a second hard drive image in VirtualBox
First create an image and attach it to your VM via the VirtualBox under Settings, then Storage.
Add an attachment to the Sata controller. Add Hard Disk
Then boot up your VM and add the following line, or similar, to your /etc/fstab file. The following is an example of mounting /dev/sdb1 to foobar's home directory. The file system is ext4 with default options.
/dev/sdb1 /home/foobar ext4 defaults 0 0
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