One of the most visible new features in Leopard is Apple's integrated backup tool, Time Machine. Taking backups -- a chore that few people do and even fewer do correctly -- and making them one-click simple is bound to improve the lives of millions of Mac users who, despite being practically perfect in every way, sometimes delete files they don't mean to delete. (I know, painful but true.)
There is a lot of excitement about Time Machine, but also some confusion; reader Matteo wrote in from Switzerland to ask that we cover some basics for setting up Time Machine. Your wish; our command. Most of our answers are gleaned from Apple's feature page for TM, a worthwhile read.
Q: What is the suggested size of an external drive to be used with TM? Does it have to be at least the same size of the startup drive? Twice as big? Half as big?
A: Apple hasn't published a recommended ratio of source to target size for Time Machine, but "as big as you can afford" is a good place to start. With TM's backup approach, any files changed in the last hour are backed up -- this lets you 'scroll into the past' and see the state of your files at an earlier time. With the default hourly snapshot scheme, frequent modifications to large files will eat up disk space in a hurry. Some especially bulky and dynamic files (I'm looking at you, Entourage's main database) will probably have to be excluded from TM backups, reducing their utility somewhat.
I'd recommend a baseline of 2x your source drive for your backup drive; depending on your level of activity, that may last you for a while. TM tries to keep hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for everything older than a month -- it will warn you before it begins deleting older backups -- so a twice-as-big external should do pretty well. Apple's got a deal on a 500 GB external Iomega drive for $140 right now (thanks Evan); you can use USB or Firewire drives for TM, and even back up to another machine or to a shared/SAN volume if you've got the setup.
Q: Can Time Machine "store" the changes even if I am on the road with my Mac and then sync them once I connect the backup drive?
A: Not positive, but I believe the answer is yes, after a fashion. You won't get the same hourly snapshots that would kick in if the backup drive was connected, but TM will still note all the changed files. Once you get back and plug in, you'd get a 'catch-up' backup with all the changes between disconnect and reconnect. This means that you can't roll back to intermediate file states that happened on the road, but it's better than nothing.
Q: Does the HD have to be formatted in a particular format or can the software work with "any" HD?
A: Apple says HFS+, and that's all that's required. USB, Firewire, remote volumes, whatever you like; the TM backup is just a big folder as far as the drive is concerned.
