It shouldn't require 2x the data.
It's a concern that I brought up when we first started with file replication (around 9.0 / 8.8 I think?) - since we were using regular Soft Dist tech to lug files around & then shove 'em into their final location.
So I asked around the SDMCache + Final Location == 2x the size problem. It's solved using pointers essentially. Can't remember what the Windows term is, but in NIX land it's "symlinks" (Symbolic links). Essentially it's a "placeholder" / shortcut. I.e. - you masquerade that "file X is here" when in actual fact, it's just a pointer to file X somewhere else on your disk.
If you're (unrelated) worried about the size of SDMCACHE on your disk, you can always monitor its size & if need be clear it out & re-start the TMC service (forces a re-parse of the directory & thus a the system will be aware of what files it actually has available to offer up for peers from the SDMCACHE).
Does that help?
Thanks, that helps!
As an afterthought - this may help you along as well (if you're playing around with PPS & SDMCACHE & such):
Happy to help .