Simple question, how many bytes are in a GB? Any storage professional would say 1,073,741,824 bytes using the 1024 increment scale. It is important to realize that not all storage manufacturers use this method of binary base 2. For example, a manufacturer may list a product’s capacity as one gigabyte (1,000,000,000 bytes, a metric value) and the not 1,073,741,824 bytes (gibibyte). So all along you are thinking one thing when they are really selling you 10% less storage then you originally planned on. I have started seeing this more and more and I just want to air out some of the confusion.
Have you ever put a 300-gigabyte hard drive into a host and noticed you only get 279.4 gigabytes when you are looking at it from inside the OS? That is because the manufacturer measured the drive using 300,000,000,000 bytes. But because the operating system calculates space using a base-2 system, that 300-gigabyte hard drive shows up in the operating system as 279.4 gigabytes (300,000,000,000/1,073,741,824=279.4).
A lot of Storage Companies out there calculates capacity using Base 10 arithmetic (i.e., 1 TB = 1,000,000,000,000 bytes) like Netapp and PURE Storage. The problem with this is that when you calculate 1 TB on the 1024 byte scale instead of on a 1000 byte scale you only get 0.9 TB (0.9094947017729282 technically). So when they say 1 TB(terabyte) it really comes out to be 0.9 TB(tebibyte). Keep this in mind when looking at SANs because a manufacture could easily make you lose out on 10% of the capacity you thought it was because of a technicality.