The general rule of thumb is to do all BI storage based upon size. It causes less allocation problems.
The size of storage will change from day to day, so if you want a days storage you are going to have to over allocate space.
Look at the status (three virtual bar) button, clip storage tab. If there is any red visible, you have an allocation problem.
I have all my video stored in a single (new) folder on a single 4 TB disk drive. This way you are not wasting cpu time moving files between physical devices.