I admit that, when it comes to upgrading my Macs, I seldom follow my own advice. Yes, I have current Time Machine backups, but normally that is my only concession to safety. With Mojave and my iMac, the situation was different: I knew that the installer was going to do deeply internal things to the iMac’s Fusion Drive, changes which only a year ago Apple decided weren’t ready for the public. The chances were that something fairly global could go wrong.

I also spotted a problem with one of my most important apps, Mailsmith, the email client. I came to Mailsmith when Microsoft killed Entourage, about eight years ago. A former product of Bare Bones Software, developers of the wonderful BBEdit, Mailsmith is free but “no longer under active development”.

Choosing an email client is never easy; Entourage and Mailsmith had proved excellent over the years, and I really didn’t want to have to migrate my thousands of existing messages yet again. When Mojave was released, it was clear that Mailsmith was broken, possibly beyond repair. My hand was forced, and I finally settled on Postbox, which is proving a worthy successor.

I upgraded FileMaker Pro Advanced to version 17, as I use that for my accounts, and made sure that all other essential tools, like MarsEdit, were ready for Mojave before even thinking about upgrading my iMac.

This week, I picked a day when I could afford to take some time away from writing. I prepared my tools, turned Time Machine off just after it had made a backup, and make a clone of my Sierra startup drive – the Fusion Drive – to a 2 TB Thunderbolt 1 external disk using Carbon Copy Cloner. With slightly more than 1 TB to copy across, that took my iMac much of the afternoon.

I only have one third-party peripheral attached, a Promise Pegasus RAID drive housing my Time Machine backups. I then ensured that its software was fully up to date, and ran Disk Utility’s First Aid to check the Fusion Drive. With everything looking ready to go, I turned Time Machine back on and ran one last manual backup.

I had already copied the Mojave installer across from my MacBook Pro, so at around 1752, I ran it.

I now had a good choice of escape routes. I could keep things going on my MacBook Pro as I tried to resuscitate a crashed Fusion Drive or a failed installation. I had a complete bootable clone of my Sierra system, and Time Machine’s backups in case it was better to restore from them. Even the weather forecast wasn’t bad, and thunderstorms exceedingly improbable.

A little more than an hour later, Mojave was up and, well, sort of running. I tried to open SystHist to see what had been installed, but its icon just bounced and bounced in the Dock, forever it seemed. Time Machine said it was preparing a backup, and that was my iMac pretty fully accounted for.

I then spotted that the new App Store app wanted me to install the eleven incompatible updates which it had been holding for me whilst I was still basking in Sierra. Among them was Final Cut Pro, and around 14 GB of Xcode 10. I tried to stop them being downloaded ready to install, and decided to copy Xcode across from my MacBook Pro.

With updates pouring in on the network, and Mojave still stuck in first gear, moving anything to the iMac over the network was a total disaster. How long for Xcode’s 14 GB? How would 8 hours sound? I tried cancelling that, and copied it across on a Flash drive instead. I then realised, and confirmed with T2M2 and Consolation, that much of this behaviour was down to Time Machine running a deep scan, as I have detailed here. I stopped that backup by turning Time Machine off, intending to leave it to get on with that after I had gone to bed.

By the time that I did leave the iMac to get on with things, it only had to finish updating Final Cut Pro, and perform its deep scan. Those were completed by the time that I got up, and I came down to an iMac which was almost ready to use in anger. Once I had set my primary apps up and thrown a few tools at the Full Disk Access list in Privacy, it was time for breakfast.

By a strange quirk of fate, the previous weekend, my wife’s iPhone 5s had suddenly died. She had no backups, but ensured that all her data was held in iCloud. Upgrading that to an iPhone 7 was a cinch, and not a byte was bruised in the process.

There are some disadvantages to power and control.