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Update: Moving from PPC to Intel and from 10.5 to 10.6 and still keeping the backup!
Authored by: only_solutions on Dec 27, '09 04:12:10PM
Update: I just reconnected my new Intel Mac under Snow Leopard to the Time Machine backup after using that same backup of my G5 under Leopard before to transport my whole installation.

Disclaimer: Like the original hint, this is not for the faint of heart and if at all it should only be attempted after making sure there are additional backups besides the Time Machine backup we're fiddling with! I may have made grave mistakes in my conclusions and I may yet lose all data on my machine and on my backup by manipulating internal undocumented structures. It does not look like it to me at this time, but that is the inherent risk!

When I installed my new Intel Mac, I chose the offer to install it from my existing Time Machine backup. Even though the backup was from a PowerPC Mac, it went through without a hitch (well, some aditional Unix binaries had to be reinstalled separately, but that was to be expected).

So I ended up with a new Intel Mac which had basically a clone of the old G5 installation, with all applications, user data and preferences. So far so good but of course Time Machine would not have let me re-use the existing backup history across the machine swap. But we're here to not let little things like that stand in our way, aren't we? ;-)

My first step was to make an image copy of my entire Time Machine backup disk. In Disk Utility I chose Restore from my regular backup disk to a spare backup disk with the Option Erase destination active this is what makes Disk Utility do an actual image copy (A Time Machine backup would be garbled by making a file copy).

Please note that in case this spare copy was ever to be re-attached to an active machine, this hint would need to be used again, but we sure hope this won't be needed. (For me this was the better way to go, but you may be better served by making the image copy and then attaching the image copy to your new Mac instead of the original, which could then still remain with the old Mac or just be kept for safety.)

I also made an additional copy of my user folder to a separate backup medium. We're dealing with a backup mechanism here and we're making undocumented changes this is serious stuff and one definitely needs to take precautions.

So now the fun begins:

I basically used the above linked hint 10.5: Repair Time Machine after logic board changes to make the Time Machine backup accept my new machine (in the process renaming the folder within the Backups.backupdb folder on the backup drive to my new machine's name that works too!).

(Hint: I had to copy over the fsaclctl tool from the backup since it is apparently no longer present under 10.6. It worked as described, but in future it may be better to deal with the ACLs individually instead of using the sledge hammer of unhooking them completely on the entire drive and later activating them again. That is kind of crude!)

I then used this hint here to reconnect Time Machine on the new Intel Mac to the "old" TIme Machine drive with all its existing backup snapshots.

As a result, when I enabled Time Machine on the new Mac for the first time, it obviously had to do a deep traversal of the virgin file system (from Time Machine's point of view) and it predicted a pretty hefty backup size, but it nevertheless accepted the G5's backup snapshots as legitimate basis and ultimately just backed up about 17GB after all, which is in line with a completely new system (Leopard -> Snow Leopard), some changes in the folder structure I made between the two machines, a newly converted mail base under Snow Leopard plus some work I've done between migrating to the Intel Mac and actually reconnecting Time Machine again.

I guess I'm not the only one to switch from a PowerPC Mac to an Intel one and in the process migrating from Leopard to Snow Leopard and I'm probably not the only one who'd be bugged by losing one's entire Time Machine history over that.

But at least at this point it looks to me as if there's actually a way to move and to still keep the time line intact and usable. I just hope messing with the internals won't still bite me somewhere down the road... 8-) (I'm keeping an eye on the backups actually being made correctly now one cannot be too cautious!)

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Update: Moving from PPC to Intel and from 10.5 to 10.6 and still keeping the backup!
Authored by: only_solutions on Dec 27, '09 06:46:43PM

Addendum: After the first incremental backup the next backups were empty despite changes being present on the Mac.

A restart of the Mac apparently cured that as well. Which sounds like a good idea anyway when making such changes.

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