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I'm running a Mid-2011 Macbook Air, my first Mac. When I bought it, it had Lion pre-installed. Yesterday I picked up an external hard drive, and made my first Time Machine backup. In the next few days I plan on going to Mountain Lion, but am trying to be cautious.

If I have issues with Mountain Lion, and want to revert to Lion, what steps can I take now to ensure that I don't lose anything when going back to Lion? Will a Time Machine backup + the Lion Recovery disk maintain all my documents/data/settings? So, I'd have a Time Machine backup of my post-update Mountain Lion system, will Lion/Time Machine be able to take all the documents and data that were created under Mountain Lion and restore them to my system after reverting to Lion?

Essentially, I'd like to know what other steps I can take now, while I have Lion, that will make this hypothetical reversion a smoother experience. Is my plan of Time Machine + Lion Recovery disk fundamentally flawed in some fashion?

edit: As discussed in the comments, I've made a TM backup, and made a Lion Recovery disk. I went forward with Mountain Lion's install. I see in the Mac App Store, that I have ML available to redownload, but there's no option there for Lion (which I was sort of expecting, but now have confirmation). Looks like the only way to reinstall Lion at this point is to use that recovery disk.

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I see a similar 'how to go from ML to Lion' question was closed, but that one seemingly was closed due to ML being beta at the time? –  Keen Jul 25 '12 at 18:27
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Exactly. Perfectly on-topic question now! –  Daniel Lawson Jul 25 '12 at 18:28
    
Do you even have a Lion recovery disk? Do you mean a physically separate disk or the recovery partition? Because the latter is likely updated to be a ML recovery partition by now. –  leberwurstsaft Jul 25 '12 at 19:11
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I don't know about that, but Carbon Copy Cloner offered to install a recovery partition on my backup disk. So I made a full backup, tested booting from it, and then went ahead to upgrade to ML. Everything went fine, so far I'm happy with it. –  leberwurstsaft Jul 25 '12 at 19:26
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I'm not sure if you can restore a Time Machine backup created on a newer version of OS X to an older version. For example, if you create a TM backup from Lion, upgrade to Mountain Lion, then create another TM backup, you might not be able to restore that backup to a Lion system. –  daGUY Jul 26 '12 at 15:16

4 Answers 4

The Time Machine backup should do a pretty good job keeping all of your documents and most of your settings and should be backwards-compatible*, but I recommend making a complete, bootable backup of your previous system so that you're guaranteed to be able to restore your machine to exactly as it was before updating.

I'm a fan of Carbon Copy Cloner (free trial) for making the backup. Back up to a clean disk or partition using CCC and tell it to copy everything. It will also help you clone your Lion Recovery HD onto the backup disk.

Once the backup is done be sure to try booting from it to make sure everything worked.

*Should be, but I haven't personally tested.

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Exactly. Better safe than sorry. –  leberwurstsaft Jul 25 '12 at 19:26
    
Note: Another alternative to Carbon Copy Cloner is SuperDuper!. –  Ed Brannin Jul 26 '12 at 23:30
    
Proceed with caution. If application support and other user data is upgraded for Mountain Lion, some of that data may be seriously incompatible with Lion, and the incompatibility may be not immediately apparent. Comparison: Downgrade 10.7.1 (Client) to 10.7 – "avoid downgrade". –  Graham Perrin Sep 13 '12 at 20:46

The combination of four questions is good, but that number – and the major differences between the operating systems – makes it difficult to give a single concise or comprehensive answer.

Some of the four here overlap with questions elsewhere in Ask Different. I'll focus on two …


Will a Time Machine backup + the Lion Recovery disk maintain all my documents/data/settings?

For this case, considering the unknowns, I should say no. Apple's standard exclusions apply.

If you encounter a problem relating to downgrade, and if you wish to use logs for diagnosis, the required data – the logs – may be not amongst your backups.


If I have issues with Mountain Lion, and want to revert to Lion, what steps can I take with Lion to ensure that I don't lose anything when going back to Lion?

If your concerns include consequences of a major downgrade from Mountain Lion – consequences such as loss or multiplication – then you must think beyond actions in Lion. Think also of …

Actions to be performed in Mountain Lion

At least:

  • for each Apple app included with the operating system that you will use in Lion, see whether its equivalent in Mountain Lion can export to a suitable format.

Application-specific formats that are designed for export and import

To minimise the risks associated with downgrades, I guess that:

  • an archive produced by Calendar in Mountain Lion should be usable without issue in iCal in Lion
  • an archive produced by Contacts in Mountain Lion should be usable without issue in Address Book in Lion

– and so on, but see below concerning potential duplication of data.

I can't guess what apps you might use so I'll list only those two.

Mixtures of local and remote data

If your Calendar 6.x stores calendar and reminder data both on your Mac and on servers – CalDAV, Exchange Web Services etc., then for downgrade purposes you may wish to produce two archives – one with service accounts such as iCloud enabled, another with service accounts disabled.

The second, smaller archive may be a more suitable starting point for import to iCal 5.x.

(I can't predict how iCal will deal with potential duplication from a larger archive that includes data from servers.)

And so on, for Contacts and for other export-enabled apps that can use services such as iCloud.

Hint

If you use iCloud alone, without using your Mac for local primary storage:

  • Apple's use of CalDAV and CardDAV should effectively remove any concerns you may have about downgrade compatibility of local archives and application support data from Calendar and Contacts.

All things considered

I should paraphrase advice given elsewhere:

  • please do not assume that a major downgrade will be entirely free from difficulty.
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Once install Mountain Lion, the recovery will be replaced with Mountain Lion recovery. What you can do is that:

  • Boot into recovery mode and format your SSD.
  • Reboot and wait for your machine to download Lion Recovery again from Internet.
  • Use Lion recovery to recover your Mac.
  • Use TimeMachine backup to restore your documents.
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Machines with 10.8 installed from factory do not take kindly to downgrade attempts. Even with a fresh SSD and multiple USB boot drives of older versions of OS X I was unable to boot. Seems the firmware will only accept 10.8 in the newest Macs.

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The machine had Lion, not 10.8, preinstalled. –  Graham Perrin Sep 13 '12 at 20:38

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