Defining Disk Space
A comparison of usable drive space to physical disk drive capacity.
Overview: There are two main factors affecting your total system storage capacity:
- RAID Overhead
- Conversion between Binary and Decimal Byte “Equivalents”
In some cases, the overhead is 50% of the total hard drive capacity.
Comparing Binary and Decimal Equivalents:
The following Table charts common Binary/Decimal Values:
RAID Overhead:
With Raid 1 (Mirror) or Raid 5 (Strip Set with Parity), a certain portion of the disk space will be used for redundancy thus it will not show up as usable space.
Example of NAS 6000 Capacity Calculations:
The NAS 6000 base unit has twelve 160 GB hard disks. Intuitively one would expect to have a total of (12×160GB) 1.92 TB storage space. Below is a calculation in Table 3 & 4 to compare physical drive space to the usable disk space available with the Windows Operating System.
Table 3
The above number representing the total number of bytes (characters) that can be stored on the hard drive. This is a decimal number, to convert this number to the decimal equivalent of the binary Megabytes (MB) or Gigabytes (GB), this value must be divided by the decimal value of a binary MB or GB. The decimal equivalent of 1 MB (220) is 1,048,576 and 1 GB (230) is 1,073,741,824.
Table 4 – Using the results from Table 3:
The available user space reported by Windows is 1,512 GB on a base unit and 1,526 GB on an expansion unit.