well... if currently you have around 500GB to backup, and you will have a laptop too - so that'd be around another 200GB more, and taking into account that any hard drive must be left with 10-15% space free to work properly... the you'd need
at least 1TB.
But remember there are two kinds of backups:
a) Incremental/historic Backups, such as time machine, that makes a security historic backup of all your files, even those that are deleted, but is not bootable.... as the external drive fills up, it will delete older copies of files.
And b) bootable clones, that take a snapshot of all your files, including system and apps, at the time of the backup and that is bootable. IMO a bootable clone is mandatory, and a Time Machine backup is optional, but thats depending on your workflow and preferences.
The best would be to have
both: a Time Machine backup for files, running all the time, in case you accidentally delete something or your machine suddenly goes to hell, so you have a backup of the latest file to the minute... and a clone (or bootable backup) updated weekly, to make sure you have a backup of all your apps and preferences. That way, if the worst happens, you have a way to boot into the system and apps in another computer, and access your files, and restore everything in a wink of an eye.
So... back to the external drive size... if you want to have both kinds of backup, I'd suggest you get 2TB. The more space, the better, and the price difference is small. Now, regarding Firewire and/or USB, I'd go with one that has FW
and USB... but you can save a few bucks by going with a USB-only drive, and apart from the read/write speeds, you dont loose much.
This and
this seem to be good basic alternatives - the
second one having both USB 3.0 and 2.0, so its kind of "future-proof", even when macs dont support USB 3.0 for now.
cheers!
