Formulas

The following formulas can be used to calculate storage (optical, tape, or both) estimates.

Note: The term "cartridge" in the following formulas refers to optical disk cartridges and tape cartridges. If you are only using one type of medium within your installation, simply calculate according to the needs of your storage management policy. If you are using both optical and tape storage, consider cartridges needed for both media when calculating the formulas in Table 1.

Table 1. Formulas for calculating storage requirements
Consideration factor	Calculation
Cartridges per day	# cartridges required per day equals: # megabytes written per day ÷ # of megabytes per cartridge where: # of megabytes written per day equals: objects created per day x object size in megabytes.
Cartridges per year	# cartridges required per year equals: total # of cartridges per day x workdays per year
Shelf-resident cartridges	# shelf-resident cartridges equals: # cartridges required per year x retention period in years
Storage group adjustment	storage group adjustment equals: # of storage groups x # of active drives Therefore, total number of cartridges required per day equals: # cartridges required per day + storage group adjustment
Libraries for library-resident cartridges	# libraries required to hold library-resident cartridges equals: # of days library resident x (# cartridges required per day ÷ # slots in the library)
Note: # indicates a total number x indicates multiplication ÷ indicates division + indicates addition