They say you never know if you have a real backup until you try to use it. They’re right.

TL;DR

• Don’t encrypt your drive until you’ve restored your data
• Don’t exclude things from Time Machine backup

The details

I sent my 2017 MacBook Pro to Apple because the keyboard was acting up. And as long as I was at the Genius Bar, I thought it’d be a good time to mention a weird problem I’d had when using Screen Mirroring on my Apple TV (moving the cursor would reveal things lower in z-order – it was weird); the Genius duly wrote that down and sent my machine to the depot for repair.

A few days later, the machine was back in my hands; not only had they replaced the keyboard and the top case (as I’d expected), but they also had replaced a few other parts – and they’d either wiped or replaced the SSD, so I had a virgin installation of Mac OS and none of my data. I booted up the machine, and, for security, told it to turn on FileVault to encrypt the SSD; then I set about restoring my data.

Plan A

I had multiple backups: Time Machine, a bootable clone drive (made with SuperDuper!), and Backblaze for offsite backup. I thought that the easiest solution would be to reboot from the clone drive and restore to the SSD, so I did exactly that.

The restore went fine, except for one small problem – SuperDuper! was unable to update the PreBoot environment. When I tried to boot from the SSD, I got a blinking folder with a question mark, which meant that the system couldn’t find the startup disk. I booted from the clone again and used System Preferences to set the startup disk to the SSD; this time, instead of the question mark, I was asked for a disk password…which, of course, I didn’t have.

Back to the clone, where I could easily mount the SSD and see its contents. Searching gave me this thread, but I couldn’t figure out how to apply the hints to my environment, so it was time for Plan B.

Plan B

I booted the “Install High Sierra” USB stick I’d kept around from last year and erased the SSD. Then I restored from my Time Machine backup. Many hours later, I was able to boot the SSD, and all seemed well.

Except…my desktop background was wrong. And my Dropbox folder was empty (though that was easy to fix by firing up Dropbox). And when I looked further, I realized that I didn’t have any of my photos, nor my iTunes library, nor my DevonThink databases. It was as if they’d never existed. But they were on the clone drive. Hmmm….

Plan C

I booted the clone and fired up SuperDuper! again. And, again, I restored the SSD from the clone, using “Smart Copy”, which found 150GB already on the SSD, and about 200GB of data that needed to be copied.

This time, when I booted the SSD, all was well – I had all of my data.

I opened Time Machine Preferences and discovered that I’d excluded my iTunes library, my Pictures folder, and my DevonThink databases from being backed up in order to save space on the drive in the Time Capsule that I was sharing among several computers. Oops. Especially since I’d stopped sharing a Time Capsule months ago and was backing up to a directly-attached 4TB drive, with plenty of space.

Conclusion

All seems to be well; I’ve removed the exclusions from Time Machine and it’s busily backing up everything now.

I haven’t checked to see if the Apple TV screen mirroring problem has been fixed – I guess I should find out, though.

I think I’ll wait a few days after Mojave ships before I upgrade; I really don’t want to go through this again any time soon!

For quite a while, I’ve noticed an odd pattern whenever I open Activity Monitor on my Mac – something was writing to my disk every 2 or 3 seconds, at a peak rate of 4.5MB/second. Over time, the total data written would climb into the terabytes (far exceeding the total data read from the disk) – but my free disk space wouldn’t diminish. Looking at the system logs didn’t enlighten me, and nothing was obvious in Activity Monitor. I’d shake my head and ignore it.

This morning, I noticed the pattern again, right after rebooting the system, and I decided to try to find out what was causing the I/O.

First step: ask Google. In particular, I asked it what process is doing i/o mac and found many potentially-useful pages. The one I chose to pursue was an Ask Different question: Which process is periodically writing to the disk? because the screenshot in the question matched mine almost exactly.

The accepted answer to the question led me to try iotop(1), but I kept getting errors from DTrace (even though I ran it as root). So I tried what looked like the next best answer, using fs_usage(1):

sudo fs_usage -w -f filesys -e grep  \
   | grep -i ' write ' > /tmp/iouse.txt

and then looking at iouse.txt showed me that a process named lssave was doing a ton of I/O. A quick Google for lssave led me to this Stack Overflow page, which led me to this macosxhints discussion, which made it clear that I needed to rebuild my Launch Services database. I used Onyx to do the job, and voilà – no drumbeat of writes!