Time Machine - Troubleshooting

C8. Backup fails after Logic Board replacement

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The logic board contains your Mac's "Media Access Control address" (or MAC Address), a unique number that Time Machine uses to be sure it knows which Mac is which.  So, to TM, it is now a different computer.

This is so it can keep each Mac's backups separate (you can back multiple Macs up to the same external disk or Time Capsule).

On Snow Leopard 10.6.x or later, you should have the opportunity to "inherit" or "reuse" or continue with the current backups, if you also restored or migrated from your backups to a new or erased internal HD.  See item #B5.  (If you're not sure what version of OSX you're running, click here).

On Leopard 10.5.x, there is a fairly elaborate way to attempt to persuade Time Machine that the existing backups really are for the same Mac:  http://www.macosxhints.com/article.php?story=20080128003716101.   It is very easy to make an error with Terminal, get no error message, and have it not work, or worse, so try that at your own risk.

But there is an alternative:  Alt/Option-click the Time Machine icon in your Menubar, or control-click (right-click) the Time Machine icon in your Dock, and select the (badly named) Browse Other Time Machine Disks option.  Select your backups, and it will take you into the normal Time Machine display, where you can see and restore from the old set of backups.

Even if you're successful with the Terminal work, your first backup with the new logic board may be a full one -- every file and folder on your system.  If Time Machine decides to do that, you cannot prevent it.

So if your Time Machine disk/partition isn't well over twice the size of the data it's backing-up, your best bet may be to just erase it with Disk Utility (in your Applications/Utilities folder) and let Time Machine start over.

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