Calculating True Drive Capacity
To effectively plan any storage project, it is important to know how to calculate true drive capacity. Although the cost of storage continues to decrease, valuable dollars can still be wasted through miscalculation of total drive capacity, resulting in the purchase of more storage than is actually needed. This is especially true when dealing with larger NAS or SAN arrays, as far too many vendors, drive manufacturers, and corresponding sales brochures round these figures off. When dealing with capacities in the terrabyte range, these seemingly small round-offs can add up to many gigabytes of storage that you’ll end up paying for.
For any spinning disk (non solid state), you’ll need to know three things:
- Cylinders
- Heads
- Sectors Per Track
The formula for calculating the total capacity is:
Cylinders x Heads x Sectors/Track x 512 = Total Capacity
The formula would result in a number similar to 20,003,880,960 (for a 20GB drive).
