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Using Mac OS X 10.7 (Build 11A511), attempts to backup volume content with Time Machine have failed.

With a simple non-encrypted image I tried three approaches:

  1. the traditional workaround, which reportedly works on Snow Leopard
  2. the removeexclusion verb of tmutil in Lion
  3. (1) and (2) combined.

This leaves the question:

How can Time Machine backup .sparsebundle volume content?

  • content of the volume, not the bands of the image.

Differences between Snow Leopard and Lion

Finder preferences

~/Library/Preferences/com.apple.finder.plist

Within this file, the FXRecentFolders key contains an array of data.

Opening the required volume in Finder, then closing the window causes volume-related data to be written as a sub-key:

  • file-data sub-keys in Snow Leopard
  • file-bookmark sub-keys in Lion.

Time Machine preferences

/Library/Preferences/com.apple.TimeMachine.plist

The removeexclusion verb of tmutil (manual page not yet published by Apple):

  • seems to add — to the IncludedVolumes array of com.apple.TimeMachine.plist — key data that differs from the data found in com.apple.finder.plist
  • does not add a corresponding key string to the IncludedVolumeUUIDs array.

Relevant commands

For a volume named myVolume

defaults read com.apple.finder FXRecentFolders | grep --before-context=1 myVolume

diskutil information /Volumes/myVolume | grep UUID

A similar question, asked in 2010

How can I get Time Machine to back up the contents of a File Vault while logged in?

  • that 2010 question focuses on FileVault 1 encrypted home directories in Snow Leopard
  • this 2011 question, not focused on FileVault, is more broadly about content of volumes attached from sparse bundle disk images in Lion.

Other references

How To: backup your File Vault home directory unencrypted (also works with Snow Leopard!) « Useful solutions (2009-12-12)

10.6: Let Time Machine backup File Vault while logged in — Mac OS X Hints (2010-01-27)

Test results

To follow.

share|improve this question
    
I wouldn't try to be too clever here. Backups need to be reliable first and foremost. Trying to hack something together that Apple has chosen not to support directly is asking for trouble. Just accept the limitations of using sparse bundles. Or migrate to FileVault2. –  Thilo Aug 5 '11 at 2:32
    
Despite great care with backups, recently I discovered that for at least one volume: the majority of Time Machine backups were useless (file sparsebundle-backups.txt at wuala.com/grahamperrin/public/2011/07/27/a/?mode=gallery). Thanks to the startbackup verb in tmutil we might somehow automatically backup every time any volume is unmounted (I thought first of unsupported MarcoPolo, but it does not recognise eject/unmount) … hacking of a different nature. I'd like to explore multiple hacking avenues with focus on Time Machine. –  Graham Perrin Aug 5 '11 at 7:13
    
FileVault 2 is not applicable to anything other than the startup volume. (This question is broader than the home directory-focused question that was asked in 2010). I could encrypt using Core Storage, but any such volume will be unusable with Snow Leopard or less. For support purposes I most often need to use my removable media with machines without support for Core Storage, machines that do work with encrypted disk images. ICT support and encryption aside, there remain a variety of other use cases where sparse bundle disk images are desirable or required. –  Graham Perrin Aug 5 '11 at 7:24
    
Graham - could you edit this a bit? It's really TL;DR –  bmike Aug 9 '11 at 21:41
    
@bmike agreed. I'll put the test results elsewhere then sit on it for a few days before another edition … –  Graham Perrin Aug 10 '11 at 4:54
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