hoakley September 18, 2017 Macs, Technology

High Sierra: Should you reformat your startup disk now?

If you have decided that you will be upgrading to the first release of High Sierra, an important question is whether to reformat your startup disk now, and if so, whether to use Sierra, the last High Sierra beta, or (if you can) the current Golden Master of High Sierra.

Apple has not yet given any explicit advice on this, but from what it has released so far, the answer depends on what type of drive your Mac boots from.

If your Mac starts up from an SSD (alone, not in a Fusion Drive), then installing High Sierra will convert that drive to APFS format. You have no choice about that. If you have been running beta releases of High Sierra on it, the version of APFS may still need to be updated to that included in the final release, but that should not present a problem to the installer.

There seems no point in trying to force any APFS update early, perhaps from a Golden Master. The final release could still differ from that, and there is no need to get any updating done now.

If your Mac starts up from a Fusion Drive or rotating hard disk, then High Sierra will require that drive to be in HFS+ format. Apple has stated clearly that it does not support the use of APFS on drives other than SSDs in the release version of High Sierra.

If you want to prepare your Mac to install the final release of High Sierra, and your boot Fusion Drive is currently in APFS format, you will need to reformat your Fusion Drive back to HFS+ first. Apple details the process here, and I have explained it in this article.

It should not matter which version of Disk Utility you use to do this, so you could use that from Sierra, a High Sierra beta, a Golden Master, or the final release. If you install macOS in remote Recovery mode, though, you should get 10.12.6 rather than any pre-release version of High Sierra. If you want to go straight to High Sierra, of course, you will need to use a bootable installer containing that release of High Sierra, or wait to make one from its final release.

Of course, if your boot drive is currently in HFS+ format and running Sierra, the High Sierra installer will make the decision for you, and you need to nothing yet, apart from ensuring that the boot drive is in excellent working order, and well backed up.

8Comments

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1

araxara on September 18, 2017 at 6:59 am

According to the macOS 10.13 GM Seed Release Notes (https://download.developer.apple.com/Documentation/Beta_Release_Notes_Sep_14_2017/macOS_10.13_GM_candidate_Release_Notes.pdf):
Apple File System (APFS)
Known Issues
• HDD-only Macs cannot be converted to APFS. (32360337)
• Some iMacs with 3TB Fusion drives and BootCamp may be unsupported for use with APFS. (31851687)
• Some third-party applications may not correctly recognize volumes that are formatted using APFS.

So it appears that Fusion drives should work with APFS (unless they have BootCamp installed). I have a 3TB Fusion drive iMac (without BootCamp) and it was converted to APFS and works just fine.

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- 2
  
  hoakley on September 18, 2017 at 7:05 am
  
  Thank you: at least it looks like they’re close to completing support for Fusion Drives.
  It sounds like that GM is yet another beta-test.
  Howard.
  
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3

Tony on September 18, 2017 at 10:43 am

Thanks for another thought-provoking item. However …

I would differ from your analysis in detail. I agree that the answer to the headline question is ‘no’ (don’t reformat to APFS in advance). I disagree that “It should not matter which version of Disk Utility you use”: some of the versions are in Beta copies of High Sierra and those should not be trusted for operational (non-test) systems.

They should not be trusted in principle as they are from a Beta release; a Beta version is an incomplete and lower-quality version of a product. They should not be trusted in practice because we know that Disk Utility has been fundamentally modified to provide APFS functions and who knows what was broken in that process. Apple’s level of regression testing has clearly declined in recent times and the APFS team is clearly under pressure, these are not good omens for software quality.

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- 4
  
  hoakley on September 18, 2017 at 12:14 pm
  
  Is there any evidence that the betas or GM have made any changes in HFS+ support? I very much doubt it: I suspect that the Disk Utility code for formatting in HFS+ (which is what I am referring to) has not changed from the first beta to the GM.
  As for doing anything in APFS, that would be a different matter.
  I also suspect that Apple’s regression testing for HFS+ is pretty mature now.
  In principle I would agree about betas. In practice I don’t think that it would make the slightest difference in the case of HFS+.
  Howard.
  
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5

Tony on September 18, 2017 at 2:16 pm

My concern is with unintentional changes: a shared method tweaked here, an enhanced data structure there, a mistaken paste over there and behaviour changes but only in a circumstance you didn’t anticipate so didn’t retest (i.e. regression test DU). I admit I’m being very risk averse here but why take chances you don’t need to?

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- 6
  
  hoakley on September 18, 2017 at 6:04 pm
  
  If you have been running High Sierra beta on an internal Fusion Drive, it may be your only option without making an external boot drive, or performing remote Recovery.
  I haven’t checked the most recent versions of Disk Utility, but older ones always relied on command tools to actually do things like formatting and First Aid. Those separate code for different file systems quite clearly – in the case of First Aid, they’re actually separate tools. Any software release can always munge a tool like that, but in the case of good old HFS+ I think the chances are very small indeed.
  It would be a lot easier than having to download Sierra’s Installer, make an external boot drive of it, restart from that, and run Disk Utility from there, I think.
  Howard.
  
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7

Alex on September 19, 2017 at 7:23 pm

After running with my internal APFS 3TB Fusion drive since the start of the High Sierra Beta period, I decided to switch the drive back to HFS+. The main reason is that the final GM candidate will not load on the APFS volume, since it’s no longer supported (they may add support in the future). Rather than being left behind in the future High Sierra upgrade cycles, I bit the bullet and reformatted my drive and restored everything from backup. Luckily I only have about 1TB of files to restore, since I keep the really large files on an external HFS+ drive. This took about 10 hours which included making a current backup, reformatting, restoring with TimeMachine and downloading and installing GM High Sierra.

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- 8
  
  hoakley on September 19, 2017 at 7:40 pm
  
  That’s an awful lot of time to have to spend after running the beta. I suspect that many beta-testers may not be so keen in future, because of problems like this.
  Interestingly, I was starting to hear reports that the GM might have supported APFS on Fusion Drives – thanks for confirming that it doesn’t.
  Howard.
  
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