Occasionally, storage devices will display sizes smaller than what the device sticker shows as the correct storage size. For example, a 785GB drive may only show ~731GB in the Operating System. This problem is related to the conversion of GiB to GB. The section below describes.
The Gibibyte (GiB) is one of the standard units used in the field of data processing and data transmission (along with mebibyte (MiB), kibibyte (KiB), etc.). Gibibyte, mebibyte, and kibibyte are defined as powers of 2. 1 GiB equals 230 bytes or 1,73,741,824 bytes. Gibibyte is closely related to gigabyte (GB), which can be a synonym of gibibyte or can refer to 109 bytes or 1,0,0,000 bytes in accordance with International System of Units (SI).
A Gigabyte (GB) can have different meanings in different contexts. When referring to computer memory, gigabyte is always a “power of two” - 1,73,741,824 bytes, but when measuring hard drive capacity it is often defined as 1,0,0,000 bytes. Generally, operating systems calculate disk and file sizes using binary numbers, so a new 500 GB drive you've just purchased would be reported by the OS as '465.66 GB' (meaning 465.66 GiB).
A Source and usable space calculator can be found at the following web location: http://wintelguy.com/gb2gib.html.
This means that when you have determined the usable space for a storage device, you will end up with roughly 93% of the total GB size. For example, 93% of a 785GB drive is approximately ~731GiB.
This can come into play when presenting a LUN (such as with the ION Data Accelerator platform) to a system. 500GB is the size of the drive in GB but when you present a LUN to a system, the OS will display ~466GiB instead.