The easiest place to start is by working out how much space 1 hour of footage will use.
First you will need to know how much footage a given size card will fit on it. You can find this out by viewing our tapeless recording times article in this section.
Divide the capacity of the card by the amount of minutes it will hold and multiply by 60.
For example, a 32GB SxS Card will hold 100 minutes of 35mbs footage. 32 divided by 100 x 60 = 19.2 so for every hour shot you will need 19.2GB of hard drive space.
Once you have this information it is a simple case of multiplication to work out how much storage you will need for your shoot.
GB per hour x number of cameras x number of days. Remember to multiply this by two if you require a second back up.
To work out how many hard drives you need, divide your total by the capacity of the hard drives you will need
Bear in mind that the storage available on the hard drive is never quite the size of the hard drive e.g. a 2TB drive actually only has 1865GB of available storage.