Another June has come (and gone), and with it the promise of a new, improved version of macOS. In this case, macOS 10.15: Catalina. Sounds so refreshing, doesn't it? Cool breezes, beautiful sunsets, pristine beaches along an endless coast.

But no matter what the imagery looks like, it's a time when I sit at Shirt Pocket HQ, braced for the inevitable news that it's going to be a long, hot summer. In my office. Drinking a lot of coffee.

Thus, in preparation for a lot of upcoming changes, we released v3.2.5 of SuperDuper to wrap up the work we did over the past few months. That release went great, and so it's time to recap previous OS releases and look to the future.

High Sierra

Back in 2017, the announcement of APFS was a big one: it meant re-engineering a lot of SuperDuper! to support the new (and barely documented) file system, along with its new capabilities and requirements. It meant months of investigation and implementation.

A difficult trek for us, but in the end, it meant a pretty painless transition for users, and with it came new features like Snapshots.

But it took us quite a while before we had a version that could be used externally.

Mojave

macOS 10.14 brought its own challenges, and new restrictions on what data could and couldn't be accessed, how scripting could and couldn't work, etc. This required even more reengineering, and another busy summer, despite the fact that Mojave was intended as a Snow Leopard-like "cleanup" release.

But, again, with that work came new capabilities, including better scheduling, smoother operation, command-line support, Smart Wake and Smart Delete.

Unlike the Mojave version, though, we were able to release something that would work well enough pretty early in the Beta cycle.

Catalina

Before going into this, let me state what should be obvious: if you're not specifically writing software that requires you to install Catalina, you shouldn't install the Catalina beta. Really. Let those of us who have to do this take the arrows. Once everything looks great, then you can come rushing in, looking all smart and heroic, and win the day.

Right now, for "regular users", there's no winning. It's all just blood and pain.

Catalina presents more challenges. Not only is the execution environment tightened further, with new requirements and restrictions, but the whole way the startup drive works has been significantly changed.

And I mean very significantly.

In essence, the startup volume is now comprised of two different volumes. The first is the "System" volume, which is what you start up from. That volume is now entirely read-only. Nobody can write to it, except the system, and even then, only when doing OS installs or updates. Users can't write to it. Applications can't write to it.

Basically, think of it as a Catalina CD-ROM you boot from. But, like, faster. And it can be updated. And it's not shiny.

OK, so maybe that's a bad analogy, but you get the idea.

Accompanying that is a new "Data" volume. That's where "your" stuff is. It's read/write. But it's also not visible: the System volume and the Data volume are combined into a new low-level structure called a "Volume Group".

The System volume "points to" the Data volume in this group using another new feature: firmlinks. And as with writing to the System volume itself, only Apple can create firmlinks. (Well, they're "reserved to the system". Plus, additional "synthetic" firmlinks are coming for network resources, but the details of those aren't out yet.)

This sounds complicated (and it is), but it's all supposed to be completely invisible to the user. You might not even notice if you're not the kind of person who looks closely at Disk Utility. (Then again, you're reading this, so you'd probably notice.)

That said, it's not (and can't be) invisible to SuperDuper. This new arrangement presents those of us who are creating bootable backups with—and I'll employ my mildest language here; the forehead-shaped dents in my desk tell a different story—something of a challenge: we can't write to a system volume (again, it's read-only) and we can't create firmlinks.

So...how are we going to create backups? How are we going to restore them?

Yeah, right around here during the announcement is where I might have peed myself a little.

Fetch My Deerstalker Hat! And Some Dry Pants!

Rather than draw this out further, after that initial panic (which always happens during WWDC, so I make sure I've got a ready change of clothes), I've done quite a lot of investigative work, delving into the new, mostly undocumented capabilities, many new APFS volume roles, how they all interact, and I've developed an approach that should work. It does, as they say, in "the lab".

That approach will require, once again, a huge number of changes on our end. These changes will be as extensive as the ones we had to make when APFS was introduced, if not more so. We have to take a quite different approach to copying, make understandable errors appear when the underlying system APIs provide no details, and we have to depend on a bunch of new, unfinished, un-and-under-documented things to make any of this work at all.

It also definitely means you won't be able to back up APFS to an HFS+ volume in 10.15. It's APFS turtles all the way down from here on out, folks, so if you haven't moved your backup volumes to APFS yet, plan to do so once you install Catalina.

But What Does That Mean For MEEEEE?

It's always about you, isn't it...Stuart. (Yes, you, Stuart. Who did you think I was talking about?)

Our goal, of course, is to make all of this new stuff invisible, or as close to invisible as possible. So, when you upgrade to Catalina, and you want to back it up with SuperDuper, it'll basically work the way it always has.

During development, though, this means Catalina is going to be more like Mojave. It'll be a while until we have something to share that you can use. During 3.2.5's development, we tried to come up with something "quick and (not too) dirty" that would do the job well enough to give people with the early betas some coverage, and it just couldn't be done to a quality level we were happy with.

We don't want to release something that we aren't confident will work reliably, even if there are some limitations. That'd be bad for you, and bad for us. So for now, if you're on an early Catalina beta, use Time Machine (and cross your fingers/sacrifice a chocolate bunny/pray to the backup gods).

So far, while we've validated the general approach, we've run into a lot of problems around the edges. Catalina's file system and tools are rife with bugs. Every time we head down one path, we're confronted with unexpected behavior, undocumented tools, crashes and failures. While we're reporting things to Apple, we're two betas in now, and it's not getting better.

Yet. Which is important, as it's still early days. No doubt Apple's exhausted engineers are barely recovered from the push to get stuff ready for WWDC (working to hard dates is never fun; we've all been there), and typically Developer Beta 2 is just "the stuff that we couldn't get done for WWDC that we wanted in Developer Beta 1". And—hey!—Developer Beta 3 just dropped, so who knows!

Anyway, we're forging ahead, confident in our approach. When we have something we will, as always, post it to the blog...and I'll be sharing any interesting trials and tribulations along the way.

When I'm done banging my head against my desk, at least.