What happens to a server’s capacity when a disk cartridge is added?

The amount of new storage you get when you add a disk cartridge to a Premiere line 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 Cinema One (1st generation), 1U or 5U Server because of its hot spare disk cartridge.

For Cinema One (1st Generation), 1U and 5U 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 5U Server with seven 750 GB Disk Cartridges uses one 750 GB Disk Cartridge for parity information. If you add a 1 TB Disk Cartridge, then 250 GB will be used for additional parity information and the storage capacity of the server will increase by 750 GB. If you add another 1 TB Disk Cartridge, no additional parity information is needed and the storage capacity of the server will increase by the full 1 TB.

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 3 TB Disk Cartridges has one 3 TB Disk Cartridge for parity information and one 3 TB Disk Cartridge reserved as the hot spare. If you add a 4 TB Disk Cartridge, then the 3 TB hot spare will be added to the array, and the storage capacity of the server will increase by 3 TB. The new 4 TB Disk Cartridge will now be the hot spare. If you add another 4 TB Disk Cartridge, then 1 TB of it will be used for parity information and the capacity of the server will increase by 3 TB. A 4 TB Disk Cartridge will still be the hot spare. If a third 4 TB Disk Cartridge is added, no additional parity information is required and the storage capacity of the server will increase by 4 TB.