hoakley September 15, 2017 Macs, Technology

High Sierra: APFS “not supported” on Fusion Drives

In an undated advisory note to those who took part in the High Sierra beta-testing programme, Apple has warned that it will not support the use of APFS on Fusion Drives in the initial release version of High Sierra. That note recommends that anyone who converted their Fusion Drive to APFS during the the beta programme should format that drive in HFS+ before they install the release version of High Sierra.

That note also reveals that:

Apple intends that a future version of High Sierra will support APFS on Fusion Drives. It makes no comment about support, present or future, for conventional spinning hard drives.
High Sierra will be released from the App Store in an app named High Sierra Install Assistant, probably instead of a normal macOS Installer app. When run, that app creates and mounts a volume named InstallAssistant containing the Install macOS High Sierra app.
The version of APFS in High Sierra release differs from that/those in beta releases.
A bootable installer for High Sierra requires a minimum of 10 GB storage. Previously 12 GB was specified.

In the preamble to that note, Apple states that, because APFS on a Fusion Drive “is not supported in the initial release of macOS High Sierra, we recommend that you follow the steps below to revert back to the previous disk format.”

As High Sierra doesn’t offer any non-destructive method for reverting a volume in APFS back to HFS+, that note next describes two methods for formatting a startup Fusion Drive as HFS+, before installing High Sierra and restoring the volume from a Time Machine backup.

The first reveals that Apple will be releasing High Sierra from the App Store in the form of an app named High Sierra Install Assistant, which can be used to create an external bootable installer (a process which I will document separately) or to install High Sierra. It is likely that this will replace simpler macOS installer apps of previous upgrades.

At present, the second method appears incomplete. Step 3 states:
On a Mac running 10.12.5 or later, use the Terminal app to run the following command:
then fails to give the command before moving on to step 4.

Anyone tempted to format their Fusion Drive in APFS then install the release version of High Sierra on it should think again. It is most probable that Apple has deemed this combination to be unsupported because of continuing problems in this first release version of APFS, not because of problems in converting Fusion Drives from HFS+ to APFS. ‘Unsupported’ could mean that you risk not only losing your data, but possibly even damaging the Fusion Drive.

(Thanks to Garry for kindly providing the link.)

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1

iawhciwc on September 15, 2017 at 6:00 pm

Have installed High Sierra beta on to machines. One a MacBook Air and no hiccups. Second Mac was a MacBook Pro 2010 17″, no hiccups during installation but found that once installed the keychain does not work. Thankfully I hardly use it. I also found the Preferences in the keychain has changed and you can no longer “Show keychain in the menu bar” in High Sierra. It was a nice feature that when getting up from a mac I could lock it and walk away, now I have to find another alternative.

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- 2
  
  hoakley on September 15, 2017 at 6:04 pm
  
  Thanks for that information.
  Although I suspect their APFS will be updated when you install the release version, at least they will both carry on using APFS.
  I pity those beta-testers who had converted their Fusion Drives to APFS, and now have to format and install afresh using HFS+.
  Such are the joys of testing betas, though.
  Howard.
  
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- 3
  
  Ben G (@fuzzylogiq) on September 18, 2017 at 12:03 pm
  
  https://swissmacuser.ch/new-lock-screen-feature-in-macos-high-sierra
  
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4

iawhciwc on September 15, 2017 at 6:17 pm

MacBook Pro 2010 17″ is still using HFS+ since it is a spinning hard drive. MacBook air is using APFS since it is an SSD. My MacBook Rp 15′ has an SSD but the one I use as my primary working computer has a Fusion in it and ever since they have been beta testing High Sierra there has always been the threat that Fusion Drives were not going to be supported, now initially and some place down the road they will be which is probably why the 25th release date rather than next Tuesday when the iOS update comes out. How long that road is and how many hairpins turns and speed corners they have to negotiate is anyone guess. They might have to create another layer between the Fusion and SSD so as to pass information between the two and I think Apple is probably wishing they had stayed away from Fusion Drives altogether.

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5

Eric L on September 16, 2017 at 4:11 am

Can i just restore from time machine to regular sierra when it wasnt running apfs. And then install high sierra gm?

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- 6
  
  hoakley on September 16, 2017 at 4:55 am
  
  Unfortunately not. Restoring from a backup doesn’t change the underlying file system – you have to initialise the volume first, which is the step detailed here. Once the volume has been initialised, as I wrote above, you can then install macOS and restore from your backup.
  Howard.
  
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7

Jed on September 17, 2017 at 3:34 pm

Like you say, it seems likely that High Sierra will support Fusion drives in a future version. I am currently on the beta and am getting that message asking me to reformat the Fusion drive (back) to journaled. I am considering waiting for the version that does support Fusion drives and simply upgrading to that. Or do you think it’s likely the Fusion drive will have to be reformatted before that?

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- 8
  
  hoakley on September 17, 2017 at 4:20 pm
  
  If you’re going to continue to use that beta, and are happy that the drive is stable, there’s no reason to reformat it now. I have no idea whether it will then need to be reformatted to take the later release of High Sierra, and we probably won’t know until that arrives.
  Of course if you’re going to upgrade it to High Sierra release before that supports APFS on Fusion Drives, you’ll need to reformat in HFS+, as you would if you were going back to Sierra.
  I don’t think that anyone knows when High Sierra will support APFS on Fusion Drives either!
  Howard.
  
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9

Tony on September 18, 2017 at 10:26 am

At first sight, I’m a little surprised that APFS does not show benefits on spinning HDs yet, even though Apple says that it is optimised for SSDs. The removal of journalling, for example, feels like a benefit to every write operation (and perhaps to start-up) that ought to deliver benefits on any medium. Or is APFS only ever expected to be adequate on physical disks and not show any significant gains – hopefully that would still leave Fusion Drives with a net improvement.

Are there any benchmarks from real systems that show the gains from APFS on SSD-based Macs?

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- 10
  
  hoakley on September 18, 2017 at 12:16 pm
  
  I haven’t seen any benchmarks, but there is another adage about betas: never try benchmarking them, as you know there will be all sorts of code there that will be removed for the release.
  The subjective comments that I have seen is that SSDs don’t appear to show any significant performance difference. But that is of very low reliability, I think.
  Howard.
  
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