Snow Leopard Time Machine Tweaks

Sparse bundles created by Time Machine in the latest versions of Snow Leopard are created slightly differently than they used to be. It used to be that Time Machine would create a sparse bundle with a name like “machine-name_001122334455.sparsebundle” where the “001122334455” part was your main ethernet port’s MAC address. Now it creates just “machine-name.sparsebundle”. So how does it associate a machine with the sparsebundle?

Well, it turns out they added a new file inside the bundle. Now, alongside “Info.plist” there is a new file called “com.apple.TimeMachine.MachineID.plist”. Inside this file is some info:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>VerificationDate</key>
	<date>2011-04-09T19:57:48Z</date>
	<key>VerificationExtendedSkip</key>
	<false/>
	<key>VerificationState</key>
	<integer>1</integer>
	<key>com.apple.backupd.BackupMachineAddress</key>
	<string>00:11:22:33:44:55</string>
	<key>com.apple.backupd.HostUUID</key>
	<string>01234567-1234-5678-9abc-12345678abcd</string>
</dict>
</plist>

The “com.apple.backupd.BackupMachineAddress” is where the MAC address is now stored, but there’s one other extra field: “com.apple.backupd.HostUUID”. This value can be found by launching “System Profiler” (hold down the option key while selecting the Apple menu to get there quickly). On the first page (titled “Hardware Overview”) is something called “Hardware UUID”. This is what goes in the HostUUID field.

So if you ever need to create a Time Machine sparse bundle from scratch, you’ll need to make this file and fill out those 2 fields. There are some other fields in there but I have no idea what they do. I think they have to do with when “fsck” was last run on the sparse bundle and whether or not the bundle is valid, but I haven’t explored it yet.

2 thoughts on “Snow Leopard Time Machine Tweaks”

  1. I’ve got my backup file corrupted and then I fixed it via fsck_hfs. After that the backup was not being possible to be used still with Time Machine: it kept asking for making a new backup, even though both fsck_hfs and Disk Utility verifies would say the disk image was fine.
    I got it paired again to my computer by changing a couple of entries in this file: there was another property added to it: RecoveryBackupDeclinedDate which I got rid of, and the property VerificatonState was set to value “2” instead of “1”. I set this last one back to value “1” and voila: Time Machine started to use again my old backup disk image. Prior to to do any new backup, I let Time Machine verify it again via “Verify Backup” which can be found on the drop down menu of Time Machine menubar icon once ALT clicked.

  2. Thank you, this tip and the comment beneath helped me on Lion 10.7.5.

    I was trying to get a computer to backup to a sparsebundle on a local/external drive (so that I could clone the sparsebundle to another backup).

    I didn’t need the MAC ID but I needed the correct UUID found as instructed in the original post and I needed to set VerificationState back to 1 as explained in the comment.

    THANK YOU!

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