iMac 27-inch, Late 2013, macOS up-to-date

I would like to back up my internal HDD (non-APFS) with Time Machine. Then erase the HDD. Then have the HDD replaced with a new internal SSD. Then restore from Time Machine.

Should I take precautions for the simultaneous switch from non-APFS to APFS? For example, must I convert the HDD to APFS before the steps mentioned above?

  • Time Machine backups are made on file level. The difference between file systems like HFS+ and APFS is buried below this level, so you won’t get any advantage from converting the HDD’s file system if the only reason is to move away from the HDD using Time Machine. – Melebius Apr 15 '19 at 7:16
  • Why erase the HDD? That can be another backup, if you put it in an external caddy and keep it somewhere safe. – Roger Lipscombe Apr 15 '19 at 9:07
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    @RogerLipscombe because security. If a 3rd party is gaining unsupervised access to the machine it’s a risk. – Stevetech Apr 15 '19 at 9:44
  • So put the external caddy somewhere safe, preferably offsite. Also: if someone's got unsupervised access to your machine, you already lost. Oh, and risk model: Which is more likely -- a black bag team visiting your house to steal your external HD, or you accidentally deleting something? – Roger Lipscombe Apr 15 '19 at 9:59

No, you don't need to convert the HDD. I recently did exactly what you're doing (though I installed the new SSD myself, which meant not having to worry about erasing the HDD) and didn't have to do any conversion.

But, just to be on the safe side, it would be smart to not only make sure you have a Time Machine backup but also clone your HDD to a different drive than the one that has your Time Machine backup. That way if, for whatever reason, you have a problem with restoring from the Time Machine backup, you have a fall-back plan. Better safe than sorry. You can clone the internal HDD to a second drive using Apple's Disk Utility or something like Carbon Copy Cloner. Instructions are readily available.

The other thing I'd suggest is that instead of simply restoring everything from your Time Machine backup to the new SSD you do a clean installation of macOS onto the new drive and then just restore your files and data using Migration Assistant. That way you get the benefits of a fresh OS installation along with the benefits of your new SSD.

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  • Thank you. About Migration Assistant, wouldn't that change the 'identity' of the computer? I'm thinking of iCloud, 'Where's my Mac', iTunes, App Store, other subscriptions? – Keep these mind Apr 14 '19 at 16:12
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    If you migrate right at the first OS install, before reaching the desktop, you get "you" imported intact. if you do it later, you end up with 2 accounts, new & migrated. – Tetsujin Apr 14 '19 at 16:48
  • @dhnyny What are 'the benefits of a fresh installation' -- assuming that you have a working system with stuff installed and configured just as you like it? – benwiggy Apr 14 '19 at 16:48
  • +1 for suggesting to have a backup plan. Having a backup is only useful when you are sure it will work. – Nimesh Neema Apr 14 '19 at 17:00
  • @benwiggy You don't lose the configuration when you do a clean installation because all the preferences, etc., are in ~/Library, which will get restored during migration. So there's no downside to a clean installation, since it won't make the whole process of getting the computer up and running with the new drive take longer. And a clean installation eliminates little problems that have accumulated over time that may be inconspicuous but might as well be gotten rid of nonetheless. – dhnyny Apr 15 '19 at 18:43

No - I wouldn’t do anything for the HFS -> APFS transition if you are on an SSD. This has been vetted for months across many architectures and as long as you have a backup of the data, proceed.

I wouldn’t make any upgrade without a backup, so YMMV if you go without recent backups - any change at that point might not be worth the risk - even letting the system run is a risk if you have no backups and would want any of your time or data back when it inevitably gets corrupted or fails.

My recommendation would be to move all the data to the SSD using an external bus connection and test that restarting to it works before you open the hardware and do any swap. Lots of people put the SSD in and then try to worry if the part is tested or the cables are correct. Do all the testing and data migration before you put in the drive is my main advice.

  1. Install the OS you want on the external SSD.
  2. Run Migration Assistant to move all the apps and data to the SSD (when booted off the SSD).
  3. Test things with the SSD running everything. Including set up backup of the new SSD to whatever destination you want for Time Machine.
  4. Run for a week - letting the internal HDD just be there, not even mounted if you prefer.
  5. Do the swap SSD for HDD.
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  • Sounds like a (thorough) plan. But in my case, the swap would be done by a third party who would also provide the new SSD. I believe I may have little options beside "put the SSD in and then try to worry if the part is tested or the cables are correct". – Keep these mind Apr 14 '19 at 17:03
  • @Keepthesemind You should be fine then. Do you want to pay them to move the data or do it yourself? – bmike Apr 14 '19 at 17:04
  • Myself. Company (ie, confidential) data. – Keep these mind Apr 14 '19 at 17:05
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    @Keepthesemind Then have them put in the SSD and test it. Know your return policy and consider enabling FileVault before you migrate any confidential data on to the SSD. There’s no secure erase other than cryptographic erase on SSD so you should be set to migrate later once you’re sure the hardware works with a vanilla OS on it. – bmike Apr 14 '19 at 20:32

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