When I compress a file multiple times, are they compressed multiple or just single time?

[sfc9982]

Are they "marked" for compressed, or really compressed?

[sfc9982]

I didn't find the answer from Microsoft's document.

[Iridium-IO]

They're actually compressed, and only compressed once. If you compress them with a different type of compression, then it changes the compression.

Check the file's Size on Disk in the file's properties window to see how much space it takes up after being compressed