Virtual LUN size calculations

When creating a CV, you can specify the capacity of each CV. However, rounding produces different values for the user-specified CV capacity and the entire CV capacity. To estimate the actual capacity of a CV, use a mathematical formula. The following topics explain how to calculate the user area capacity and the entire capacity of a CV.

The CV or LDEV capacity consists of two types of capacity. One type is the user area capacity that stores the user data. The second type is the capacities of all areas that are necessary for an LDEV implementation, including control information. The sum of these two types of capacities is the entire capacity.

Implemented LDEVs consume the entire capacity from the parity group capacity. Therefore, even if the sum of user areas of multiple CVs and the user area of one CV are the same size, the remaining free space generated when multiple CVs are created can be smaller than the free space in the parity group when one CV is created.

When using the CCI, the specified size of CVs is created regardless of the capacity calculation. Therefore, even if the same capacity size (for example, 1 TB) appears, the actual capacity size might be different between the CVs created by CCI and the CVs created by Device Manager - Storage Navigator .

If an LDEV is created by the Create LDEVs Window, depending on the specifying of the offset boundary option, the capacity of LDEV differs even if the specified value is the same. If the Offset Boundary option is selected, the specified capacity of LDEV is offset conforming to the prescribed boundary values, and an LDEV is created. For details about the prescribed boundary values, see Calculating volume size (CV capacity unit is MB), Calculating volume size (CV capacity unit is blocks), Calculating fixed-size volume size (CV capacity unit is MB), or Calculating fixed-size volume size (CV capacity unit is blocks). If the Offset Boundary option is not selected, the LDEV whose capacity is the specified size is created.

In the storage system, data is managed based on a slot, and data protection is performed based on a parity stripe unit. For an LDEV whose capacity is offset by a boundary, the efficiency of the drive capacity is improved because the capacity of LDEV is offset by the unit of the data management. If you emphasze the efficiency of the drive capacity, select the Offset Boundary option when creating LDEVs. If you want to have the LDEV whose capacity is the specified size, do not select the Offset Boundary option when creating LDEVs.