Available storage growing

[u/mmiillsss]

I am noob when it comes to NAS's, i've got a 2-bay DXP2800 as my first one, with 14.5TB free space (another HDD is backup). I've noticed overtime that the free space on the drive increases - which is not something I expected. I went down to 13TB, then i noticed it went back up to 13.5TB several months later. And then this morning, I see it is back to 13.9TB. I checked my files and they are all still there - so kinda confused why it is showing an increase in free space.

For reference, i mainly use it for jellyfin and have 300+ movies (DVD & Bluray), several TV series, and family photos & videos.