A certain absurdity is possible when transferring a file over scp between two filesystems that support transparent compression, e.g., btrfs: File is stored compressed with zlib (other options possible; this is the most absurd). Uncompressed by a kernel module to make it visible to userspace program. scp compresses the file with zlib for transmission over the wire. Receiving scp unconpresses the file, then writes it to the filesystem. Kernel recompresses the file with zlib to write to the compressed filesystem.