What happens to the capacity of a Premiere server when a disk cartridge is added?

The amount of new storage you get when you add a disk cartridge to a Premiere server depends first on the capacity of the new disk cartridge compared to the capacity of the drives already in the array, and second on whether or not the server is a 3U Server. A 3U Server behaves differently than a 1U Server, because of its hot spare disk cartridge.

For 1U Servers, if the new disk cartridge is no larger than the largest drive already in the array, then the server's storage capacity increases by the size of the new disk cartridge. If the new disk cartridge is larger than the largest drive already in the array, some of the new capacity will be used for parity information. For example, a 1U Server with two 4TB Disk Cartridges uses one 4TB Disk Cartridge for parity information. If you add a 6TB Disk Cartridge, then 2TB will be used for additional parity information and the storage capacity of the server will increase by 4TB. If you add another 6TB Disk Cartridge, no additional parity information is needed and the storage capacity of the server will increase by the full 6TB.

The hot spare on a 3U Server must be able to replace any disk cartridge in the array, and so the hot spare must not be smaller than any other disk drive in the array. For example, a 3U Server with eight 4TB Disk Cartridges has one 4TB Disk Cartridge for parity information and one 4TB Disk Cartridge reserved as the hot spare. If you add a 6TB Disk Cartridge, then the 4TB hot spare will be added to the array, and the storage capacity of the server will increase by 4TB. The new 6TB Disk Cartridge will now be the hot spare. If you add another 6TB Disk Cartridge, then 2TB of it will be used for parity information and the capacity of the server will increase by 4TB. A 6TB Disk Cartridge will still be the hot spare. If a third 6TB Disk Cartridge is added, no additional parity information is required and the storage capacity of the server will increase by 6TB.