All you need to do is run a "dumb"[1] rsync to a backup provider running on ZFS, and the remote will have its own set of day/week/month snapshots - exactly like time machine[2].
Now if only there were such a provider ... standards based rsync over ssh ? Remote ZFS filesystem ? 12+ years of history providing that service ? Progressive stance on govt. monitoring ?[3] No, it would be too good to be true.
[1] Dumb, as in, just a straight 1:1 mirror.
[2] But independent - no relation to TM on your own system
One important difference between Time Machine and using rsync.net in the way you describe is that Time Machine doesn't require trusting anyone with your data[0].
Of course, it's possible to have encrypted snapshots on rsync.net with duplicity[1], the method I use. That being said, I have no particular reason to distrust rsync.net, and I have liked the service they have provided. If anything, I trust rsync.net more than other backup providers and certainly more than Apple.
[0]: Assuming Apple hasn't set up Time Machine to secretly send files back to Apple. But if you run Mac OS X, you're already trusting them not to do something like that.
Time Machine will regularly (as in once a month or two for my household of Macs, sometimes in as little as a week) complain "Time Machine completed a verification of your backups. To improve reliability, Time Machine must create a new backup for you." Apple says don't backup to a NAS. Plenty of folks have reported problems.
Getting it set up in the first place [0] keeps the selection of customers significantly smaller than those that are better off just buying a Time Capsule, or even sticking a USB drive onto an Airport Extreme (which I recall seemed to work fine). And Apple did say it's not supported. I wish they'd just fix it. IIRC, it worked reliably pre-Lion. EDIT: or for that matter, why not just bundle up the page I referenced into a nice app bundle with a pretty icon?
A more significant problem is that Synology (which is what I use) is out there saying, "Time Machine: works great with a Synology NAS!". And it does work great...until it doesn't, and last I checked Synology has no docs on how to fix it.
As for Mavericks, I'm pretty sure I've seen the problem on the one machine I have running the dev preview. Or maybe not, maybe it was before I put Mavericks on (I realize that's not terribly helpful information). The problem with saying whether it's better or not is that on my machines it may be a month or more before it rears its head. So it would take me six months or so before I could personally say that it's better for me.
Buy a Time Capsule if you want the Apple experience. It will cost you, but then it's Apple's solution.
Apple Time Machine has never been friendly to NAS other than Time Capsule. You have to do some hackery to get it setup, so the above fix steps are suitable for that crowd.
There was a technical discussion of the protocol used for networked time machine backups on the apple support pages but I can't find it back. Basicaly TM was designed to be local first, and adapted to also work over ethernet afterwards, but doesn't properly recover when you have failures (i.e. corrupted data or lost connection) at the wrong timing during the backups. From memory the network protocol changed one or two years ago to be more reliable, but the fundamental assumptions seem to have remained.
That's why it's advised you do at least your first backup with a wired connection for instance.
CrashPlan doesn't require that you use their service. The client software (which is free) is also server software, and you can backup to your own server(s).
CrashPlan's java based software just basically died on me after a while, so I switched to backblaze, which had much better performance. But people are now talking about bad experiences when they actually try to restore from backblaze. You can't win with these things it seems.
Currently I do Laptop + Time Machine HDD at work & a backup file server at home which syncs with my laptop with bittorrent sync and the file server is backed up by backblaze.
CrashPlan process in linux occasionally eats up most of the cpu. As a result of this I haven't been able to complete a single full upload after trying it for the last 4 months for a few hundred GBs. I have paid for a full year but I don't think it makes sense to renew. CrashPlan sync is just too slow and CPU heavy for a laptop that is used for dev work at the same time.
- Time machine: is not reliable for network backups (yes, really)
- CCC: needs a USB connected drive for a MBA
- Crashplan: recurring payment service based in the US
All of the above solution are useful, but none are reasonable and no brainer backup solutions for everyone, especially for MBA owners.
As for now, bittorent sync with a mirror on the same network feels like the best solution IMO.