Feature Request replicate not recursive about zfs-backup

[adaugherity]

At first I thought this wasn't possible -- that an incremental send/receive will include all intervening snapshots, but after some quick testing I realize I was wrong. Using the -i option to zfs send instead of -I will do an incremental send without including intervening snapshots. (The -R option is for a recursive send [called "replication stream" in the man page] which includes child filesystems, properties, etc. and is orthogonal to both incremental options.)

I'll have to do more testing and figure out the best way to include this option without causing problems (or at least make sure the caveats are clearly documented). I can see a potential problem where e.g. if you miss some backups, you probably do want all the intervening dailies copied next time you back up, not just the latest one.

Please note that I use zfs recv -F to remove snapshots on the destination which are not present on the source, so that when they get rotated out on the source, they also get removed from the destination rather than remaining indefinitely to clutter it up. (People have already requested disabling this option, so I do plan to make that configurable, but probably won't change the default, as I don't want to break my current workflow.)