NOTE: The process described below was that performed by the first release of the installer, which Apple has since replaced by a single monolithic installer app of 5.17 GB. Using that second version should be far simpler, and merge the initial download steps. Ensure that you make a copy of the installer app before letting it install, or you will need to download it a second time to make bootable installers, etc.
When you first start downloading High Sierra, you might think that something is wrong: it comes initially as a small install tool, Install macOS High Sierra, which weighs in at a modest 19.9 MB, but the hefty payload has yet to come.
Run that installer, and you’ll be walked through the usual licence agreement, and asked to select the disk on which to install High Sierra. By default, you’ll be offered your current startup volume. If you want to install it on another drive, click on the button to show all mounted volumes, and select its correct destination. I opted for an external SSD, as my iMac’s internal storage is a Fusion Drive, which cannot yet be converted to APFS.
Once that is done, the main download starts. Again, this fools you to begin with: despite my rural sub-broadband connection, it said that it would only take eight minutes. Just a few moments later, it told the truth, as its bulk became apparent.
The installer then creates a folder named macOS Install Data on the designated volume, into which its components are downloaded. These include:
- a 2.6 MB AppleDiagnostics disk image,
- a 491 MB BaseSystem disk image,
- a small Installer package containing an incompatible app list,
- a 5.6 GB Installer package InstallESDDmg.pkg, containing the bulk of the installation,
- a hidden and protected folder named Locked Files.
If you suspect that something has gone wrong during the download or installation phase, use the Installer Log command in the Window menu to see what the installer is up to. My first attempt at installation died quietly after downloading the first third. As its log confirmed its inactivity, I quitted the installer app, opened and ran it again.
The installation is a succession of black screens, white Apple logos with progress bars which behave weirdly, and little accurate user feedback. I counted at least five different progress bars, of which only one had any vaguely useful time estimate, and most had none at all. You’ll know that you have reached the end when a grey screen appears: that signals the start of configuration and migration. Here, that took 15 minutes from the start of the installation phase, but that does not include any conversion to APFS.
You are given no option as to whether to convert the install disk to APFS, and on this iMac, the installer made the wrong decision, if Apple’s ‘rule’ is to be believed. As I was installing onto an external SSD, I had expected it to be converted to APFS from HFS+. It wasn’t, and there is now no easy way to perform that conversion, except perhaps by starting up in Recovery mode. However, if your internal boot drive is an SSD, expect it to be converted to APFS – no choice. I do not yet know whether this is fixed in the second version of the installer.
The installation itself went fairly smoothly, but migration (of limited data from my internal Fusion Drive) was a dismal failure. The migration progress dialog is full of bugs, and never completed.
That dialog shows three indicators of progress: a progress bar, which became stuck at about 80% and never moved thereafter; a time estimate, which became stuck at 2 minutes to go; and a claimed transfer speed in MB/s, which actually incremented more like a percentage progress figure, but continued plodding past 100 without showing any signs of completion.
In the end I clicked on Cancel, which didn’t offer to cancel the migration, but to shut my Mac down. I then had to start the whole configuration process afresh. I didn’t both migrating anything the second time around, but will try Migration Assistant when I have a few hours to spare.
I had a chance to test some of my free tools out: Consolation 3 seems to run fine, as does LockRattler, even if the latter still doesn’t work properly on El Capitan.
The significant change in security data file versions in High Sierra is that the KEXT block version has risen to 13.0.0, which reflects High Sierra’s new behaviour with third-party kernel extensions.
One very important correction to Apple’s pre-release documentation is that, as far as I can see, Sierra 10.12.6 is perfectly capable of accessing High Sierra’s APFS volumes, although both the command tools and Disk Utility in Sierra are incomplete and inadequate for handling them. I have not checked an APFS drive in Target mode, which will be important to those who might want to mix and match Sierra and High Sierra systems.
Another important observation is that, as usual, High Sierra removes its installation files on completion. I haven’t worked out a way around that, to save another huge download.
Overall, particularly when I discovered that my boot SSD was still using HFS+, High Sierra seems remarkably little different from Sierra, considering it is a major version upgrade. But maybe its gems are still hidden.
(Updated 26 September 2017, following the release of the second version of the installer.)