WorpDrive storage is provisioned in blocks of a fixed size.
Each iControlWP subscription has its own configuration for the size of each allocated storage block, and how much each additional block costs.
For example, you may have an iControlWP subscription with a starting block of 150GB (153600MB). This means that included in the cost of your subscription is a total of 150GB of WorpDrive storage across all your site backups.
iControlWP will total up all the disk space used across all of your sites to find your total disk space usage at any given time.
If you exceed the initial block storage, say for example your total WorpDrive storage is now 200GB, you will be then be allocated a new storage block of the same size, bringing your total available (in this example) to 300GB (307,200MB).
Allocation of a new storage block will result in an increase of the cost of your subscription. Please refer to your subscription details for further information on the cost of additional storage blocks.