Time Machine Quotas
Quick tip for Time Machine backups: Mac OS X Server ("Server.app" these days) can setup a quota for Time Machine backups that is specific per-machine (rather than per-user). This trick works on any share, actually, since it's a root-owned property list in the share directory. You'll want Mavericks or later as a client for this to work, but to set it up
cd into the root of the Time Machine share and create the plist with (for a 500GB example):
/usr/libexec/PlistBuddy -c 'Set :GlobalQuota 500000000000' .com.apple.TimeMachine.quota.plist
On the server, make that owned by
chmod 644 et voila! You have quotas. No need for "real" quotas, LVM, or other fun. Works over SMB and AFP.