A simple solution would be to use a compressing file system on the server side. See "Allocation and layout policies" in Wikipedia's "Comparison of file systems" for a list.
Another option is to use a filesystem which offers snapshots or copy-on-write. btrfs would be a good candidate for this since it offers everything but one tiny feature: It's not safe enough for backups, yet. Don't get me wrong: btrfs is great; I'm using it for about a year, now, and never had problems. But backups need to be reliable first and foremost.
Also you often cannot simply create a partition on a server with a file system of your liking. There are two workarounds:
You can create a huge file on the server and create the file system in there (just give
mkfsthe path to the file instead of a device name). Afterwards, you can mount this file system usingmount -o loopfile mount-pointIf that's not an option but you have FUSE (Filesystem in Userspace) enabled in the server (it's a kernel module), then you can use lessfs.
Lastly, you could use a dedicated backup tool for this task. There are many options (like dar, rsnapshot or google for "linux backup"). But be warned: I searched many years, tried many options and still haven't found anything that is as simple as rsync and a powerful file system.