rsync since version 3.2.0 supports more than zlib:
--compress, -z turn on compression --compress-choice=STR, --zc=STR choose compression from lz4 (fastest), zstd, zlibx, zlib (slowest), none --compress-level=NUM, --lz=NUM zlib and zstd can be tuned with compression level zlib from 1 (lowest) to 9 (highest), default 6 zstd from -131072 to 22, default 3 Compression speeds up rsync if the the compression both manages to produce a smaller amount of data to transfer and does the compressing fast enough not to create a new bottleneck for the transfer. There are now many options to try, most faster than typical Internet connection speeds and some even faster than mass storage speeds (lz4 and zstd can be used in e.g. ZFS)