One disk image is just a file which size is equal than the size of the drive you clone.
So you need a partition/volume of a size large enough to contain such file, no matter how that volume rely on.
BUT BEWARE cloning drives...
Read my hints and tips on this argument. Check out my signature at bottom of this post
Unless you don't care too much about your data.
Technical Manager @ Recupero Dati RAID FAsTec
USEFUL RULES and GUIDELINES
1) What to check BEFORE begin a disk image/clone process [link
2) Disks that are too slow while imaging/cloning them [link
3) All my posts on this forum [link