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"My only question is: how much HD space you guys think Time Machine is going to eat? And how much stress will it put in both HD and system resources?"

The simple answer is as much (or as little) as you want. With regard to HD space, all appearances indicate that Time Machine makes one full backup, and then stores incremental changes to individual files. As for other system resources, I would guess (though I have no direct knowledge), that Time Machine uses the Spotlight APIs to get notified of changes to files as they occur. This means that files can be backed up on a per-change basis, rather than a bog-my-system-down-for-10-minutes-every-night basis. Thus I would imagine that Time Machine will have no noticable impact on the performance of reasonably recent machines. Of course, I feel the same way about Spotlight, and a lot of people complain about it slowing down their machines, so who knows. Worst case scenario, turn it off and buy a good backup tool.

The Time Machine preference panel has a selector for when it will perform backups. From that panel it would appear that it backs up files periodically (e.g. at midnight), rather than on every file change.

Actually, I'd argue that the LACK of UI changes is proof they have *something* cooking. Otherwise, I'd expect to see a little more unification.

I'm sorry, but your argument is just silly. It may well be that Apple has some new UI goodies that we won't see till Leopard is released, but please stop taking the absence of a feature that you really want as proof that Apple is hiding something! Let's take an example from a different topic:

It'd be really cool if leprechauns existed. In fact, I've never seen a leprechaun; considering that leprechauns are supposed to be really good at hiding, the fact that I've never seen one must mean they do exist! Yay!

Makes sense? No? I didn't think so.

Your leprechauns argument is silly.

It seems likely that Apple will introduce some UI changes. There is a rumor about Illuminous, so it seems it might be a possiblity. So we're dealing with a possible liklihood.

Compound that with no major changes AND an announcement from Steve Jobs that there are top secret features planned and you end up with something a bit suspicious. I think leaping to the "it COULD mean a new UI" is EASILY within reason.

In this sense, your comment doesn't really jive with the facts, and comes across as smug anyway.

Apologies if I came across as smug. My point is simply that your argument ("that the LACK of UI changes is proof they have *something* cooking") is weak.

The argument would be fine if you could also argue that Apple *not* making UI changes in developer previews has historically been an indicator of UI changes in released products. There have likely been cases in the past (though none come to mind) where Apple has kept a lid on UI changes until a product's release. But there have also been countless cases in which Apple has released a new version of a product without updating the UI. So I think its rash to make claims about what the unchanged UI means for the final release: all it really "proves" is that Apple hasn't updated the UI for the developer preview.

Exactly how it works is still up for debate. There's been a lot of discussion based on what's been available in the developer previews, but I don't see why Apple couldn't be hiding something cool up their sleeve (such as some not-necessarily-ZFS snapshot-enabled filesystem) to be announced on the release of the final product.

But regarding how it seems to work in the developer previews, John Siracusa blogged about it back in August: http://arstechnica.com/staff/fatbits.ars/2006/8/15/4995 The post is interesting, but here's the really pertinant bit:

"The upshot, as readers probably know by now, is that Time Machine is not an interface to file system snapshots built on any sort of new, modern file system. Instead, it's an automated backup system that works with plain old HFS+. The point-in-time views in Time Machine are actually sparsely populated directory trees on an external disk or server containing mostly hard links to unchanged directories, plus full copies of the few files that have been created or modified since the last backup.

"Apple added traditional hard links (that is, hard links to files) to HFS+ back before Mac OS X 10.0 was released. In Leopard, HFS+ supports hard links to directories as well—an ability wholly alien to any other Unix-like operating system that I can think of. This is how Time Machine builds its sparse trees. The very first backup is a full copy. All subsequent backups contain hard links to the unchanged portions of the previous backup."

"The very first backup is a full copy. All subsequent backups contain hard links to the unchanged portions of the previous backup."

I figured it was something like that. Nothing particularly amazing, but if it works well, great. Not enough people back up properly (including myself, hahaha.) Plus they have the typically cool Apple UI on it.

Absolutely.

We all want some cool new filesystem goodness (witness all of the buzz over a ZFS driver), but in the above post, Siracusa makes a great point: regardless of the not-so-flashy technical details, "Time Machine is 'backups made easy enough that people will actually do them,' and that's nothing to sneeze at."

Unfortunately it does look like ZFS won't be actually utilised until Leopard+1/XI. My only concern is if I change a 10GB iMovie project and Time Machine decides to duplicate the whole 10GBs. Not ideal.

"Unfortunately it does look like ZFS won't be actually utilised until Leopard+1/XI."

Yeah, although it may be too early to guess.

"My only concern is if I change a 10GB iMovie project and Time Machine decides to duplicate the whole 10GBs. Not ideal."

From http://www.apple.com/macosx/leopard/timemachine.html
Do Not Backup: By default, Time Machine backs up your entire system. But you can also select items you'd rather not back up.

I also wonder how Time Machine works and how usable it is. Maybe it works like SubVersion or other source control systems, by keeping a diffed back-up of changed files, so it uses as little space as possible. Still if you are modifying big binary files like images and videos it could get messy. Unless they have some clever binary diffing technique (which is possible.)

Text files are easy to diff because there's a common separator: lines of text. This is not possible with binary files.

What would make more sense is if TM looked at each files modified date. Lots of back up utilities do it this way as well. Regardless of how big your file may be, it's trivial to call a function to get the date it was last modified. Take that and compare it with the copy already backed up and if the former is newer, back it up.

Snapple

I didn't get the joke; I am not an english native speaker. Care to explain? (seriously!)

My guess is he meant SuN + APPLE, so you get snapple...

Snapple is a fizzy apple drink as well...

Not really that funny, but I think that's what he meant, hope that helps... :-)

I think he meant "Snapshots" (feature of ZFS) + Apple = Snapple...

Yeah, Snapshots + Apple does make more sense :-)

Oh, still not funny...