Today I got to trying out the major feature of Leopard: the Time Machine. I was postponing it because I did not have proper external storage. Although I do have several USB disks sized from 100 to 260 GB, they are not empty and to clean them would take too much time that I currently do not have. Backing up on network drive would be technically possible - with some tweaking - but copying over network is always slower than USB2 or FireWire. Besides, the drives are so cheap nowadays: I have picked the 500 GB "The Book", Western Digital in Costco (Kanata) for $149. You have to agree that one cannot resist this price and product with this name (I have a weak spot for anything Book ;-))
Time machine requires drive at least as big as the machine hard disk - which is at least 250 GB in my case. But if the whole point of time machine is to keep HISTORY of files, therefore (unless your disk is mostly empty) the only way how to do it is make the backup drive bigger. Double the size is a good start. I have asked the Apple guys what would happen when the backup drive gets full and it seems to be pretty nicely designed: when the backup space is tight, Time Machine starts purging older versions and your window back in time starts shrinking, up the point (in worst case) having a single last backup. I have not seen it yet, but it makes sense - worst case scenario is the "default" backup algorithm.
The Apple guys also mentioned that you can add additional drive and Time Machine should be able to use them together - sort of expanding the backup to new volume - as long as the are plugged in at the same time. I was expecting that after (e.g. year from now) I buy a 1 TB drive, I would need to copy the content of the old 500GB and have the new backup capacity equal to 1 TB in total, but this seems not to be case. Actually, copying is something you should NOT do - just make sure both disks are plugged in and Time Machine will manage the rest - and (assumably) if you do it soon enough, with 500 GB and 1 TB disk you will get 1.5 TB space. Well, with three USB 2 and two FW ports, I guess I can go for VERY long span back in time :-) - as long as I keep buying more USB/FW disks. If this idea takes off and Microsoft does copy this feature from OS-X as well (as they did for many others), buying stock of external hard drives manufacturers may be a good investment :-).
Time machine can be configured not to backup certain files. This makes sense for e.g. VMWare virtual hard disk image, which gets modified pretty much after each run and each backup would copy whole file - few gigabytes worth. For VM, the best strategy is to have different external hard drive (ideally formatted as FAT32 so that it can be read/written on Linux and Windows as well) and use to for VM copies only. Which is exactly what I am going to do next.
The disk is being backed up as I type this. Drive is very quiet, almost unnoticeable, even with fan inside (you can feel the air moving). Backing up 160 GB (yes, I managed to fill so much space) will take an hour or two, so we will see how the restore works tomorrow.