One thing that always gives me pause for thought when dealing with any of the new storage or HCI offerings is the discussion of dedupe or space savings. Some are presented as ratios while others are a percentage. I was recently telling a colleague I was getting 97% dedupe on some VDI workloads while he was getting 4:1 on another type of workload.
It took us a few minutes to get the maths right to work out the numbers so we could compare like for like, and so to that end I decided to create myself a little table to save my aging brain cells at a later date.
One thing that is not immediately apparent to most is that it is a case of diminishing returns the higher your ratio, hence why I have done more of the lower values and included some higher ones for completeness.
At some point I might do a little calculator that gives exact answers but as a rough and ready aid, it served me well.
Space Reduction Ratios and Percentages
EDIT: While the table above allows you to compare apples with apples numbers wise, it is not a full list of things to consider when looking at storage savings vendor vs vendor. The comment below by Rich Fenton from Nimble Storage gives a lot more insight into the other considerations. Great points and all worth considering when storage shopping.