I have enabled deduplication on a volume. I copy over the same iso 3 times (~683MB). I force a deduplication job to run from powershell (Start-DedupJob i: -type Optimization) and then the results are confusing. Hoping someone can make sense of the math here, just so i understand the process a bit better.

If I copy the same file 3 times, i would expect the ratio of saving to be close to 66% and the actual used space on the volume to be close to the size of a single copy - 683MB. Instead, I am seeing 41% ratio, and 1.88GB used space? However, the dedupe savings of 1.31GB seems right.

Has anyone played with this feature as yet than can explain why the discrepancy in the numbers? Note that the volume is empty except for the 3 copies of the iso: