On Sep 19, 2010, at 4:11 PM, Bob Stern wrote:

>> Geoffrey Heard wrote:


>> I'm about to embark on a trip using my #2 machine which, at the end of the journey, I want to leave behind me with some other gear so it can be there ready for use next time I travel to that destination.
>> 
>> Now -- what I thought I would do was back up my #1 machine to a 500 GB USB HD using Time Machine, use that to put all my stuff on the #2 machine, then during the trip, let Time Machine do incremental; back-ups from time to time.
>> 
>> When I return, I thought I would plug that USB HD into my #1 machine and use Time Machine to bring my #1 machine up to date.

> To accomplish what you want with Time Machine is complicated because it associates a given backup with exactly one Mac, based on the hardware address (MAC address) of the Mac's built-in ethernet interface.

But if what Geoff plans to do is the exact cloning, i.e. make a total backup (including System) of #1 machine and restore the backup onto #2 machine totally or vice versa, the machine identifier (no more MAC address but computer name in Snow Leopard) is ignored. From OS X Installer's "Restore from Time Machine backup", I can access backups of my MBP as well as those of my Mac mini. (Via File Sharing, an external disk connected to my mini is made available to my MBP as TM disk.)

Another method, not using Time Machine and presumably faster, would be to [1] boot from OS X Install DVD or an external HD, [2] use Disk Utility to make a disk image of #1 machine on the external HD (File:New:Disk Image from [Select a Divice]: set Image Format to *CD/DVD master* to make it bootable), [3] restore the disk image onto #2 machine. And, just before leaving #2 machine, [4] make a disk image of #1 machine on the external HD, and [5] restore the disk image onto #1 machine. 

Anyway, I think it would be safer to have two or more backups created in different ways.

Also, I'd like to recommend you to make the external HD bootable as OS X Installer for, in my experience, the optical drive is Mac's most fragile component. It's easy: [1] use Disk Utility to make a disk image of OS X Install DVD (Image format set to *CD/DVD master*) and [2] restore the disk image on a small partition on the external HD (8 GB would be sufficient).


Kino