Effective GB...
...is storage industry speak for how much storage your real physical GB is equivalent to after compression, dedupe, and any other clever tricks the hardware and software might do to increase the amount of data stored. It's a pretty subjective number because some things compress a great deal more than others (e.g. images that are already compressed...).
Sometimes they are also honest enough to deduct the overhead for reliability, e.g. erasure coding, RAIDing, etc.
Biting the hand that feeds IT
