Mike's picture by Mike | May 27, 2020

Update (July 16, 2020): Apple fixed the underlying OS issue described below in macOS 10.15.6, and the CCC 5.1.20 update puts our workaround on the back burner. Every challenge opens up new opportunities, and that's actually how we're seeing this incident in retrospect. Rather than just hoping for a fix, we invested in a solution, and that solution puts us in a solid position for the next major OS.

Update (May 29, 2020): This issue is now addressed in CCC 5.1.18, which is available for immediate download – CCC can make bootable backups of macOS 10.15.5. Choose "Check for Updates" from the Carbon Copy Cloner menu to get the latest version of CCC. Special thanks to my team members for helping put this release together so quickly, the folks at Wordcrafts for a wicked-fast turnaround on these UI translations, and for several beta testers that helped us knock out some kinks along the way.

Early last week we discovered an APFS filesystem bug in a beta of macOS 10.15.5. The technical details of the bug are laid out below, but the short version is that we're no longer able to use our own file copier to establish an initial bootable backup of a macOS Catalina System volume. To be very clear – existing backups are unaffected, and this has no effect on CCC's ability to preserve your data, nor any effect on the integrity of the filesystems on your startup disk or your backup disk. The impact of this bug is limited to the initial creation of a bootable backup.

So that's a lemon... But hey, summer has arrived here in the northern hemisphere, so let's make some lemonade!

Creating bootable backups on macOS 10.15.5

Last year at Apple's Developer Conference, Apple suggested that backup software could use Apple's "Apple Software Restore" (ASR) for cloning APFS volume groups. Initially I dismissed this – I shouldn't have to use Apple's black-box utility to do my job, I prefer to take full responsibility for my backups. Anticipating a world in which Apple continues to restrict access to APFS rather than grant it, though, we decided to invest a fair amount of time evaluating this functionality, and we've been beta testing it for the last 8 months. I don't like to lean on ASR for general backups because it has some shortcomings and doesn't give any insight into its internal activity (e.g. files copied, errors encountered), but in this very narrowly-defined case, we can leverage Apple's proprietary utility just to establish bootable backups. We posted a beta last Sunday with new UI around this functionality, and we intend to... Read More

Sarah's picture by Sarah | December 24, 2019

We will be closed December 24 and remain closed December 25 to spend the holidays with our families. We will also be closed December 31 through January 1. 

Limited staff are available to respond to customer requests until January 2. We appreciate your patience if it takes a bit longer for us to respond than is typical.

Mike's picture by Mike | October 7, 2019

We posted our Catalina-certified build of CCC way back in August, so the last few weeks have been eerily calm. Now that Apple has made the OS release schedule so consistent, we find this time of year to be a lot less stressful by simply being ready for it, on time. Since about Catalina Beta 9, the OS has been feeling pretty polished and ready for prime time. I think I have just one gripe with Catalina — Spotlight is so persistently annoying when it prevents volume unmount requests! That's a pretty trivial complaint though, and easy enough to work around. On the whole, Catalina seems to be working pretty well, and CCC is 100% ready to make bootable backups of the new read-only System volume and its Data volume sibling. If you're wondering what those are, we put together an article to explain how the new System/Data volume group works:

Working with APFS Volume Groups

Getting Ready to Upgrade to Catalina

Before you upgrade to Catalina, it is important to understand that downgrading to your previous OS will be impossible without a bootable backup of the previous OS. Before you apply the upgrade, we recommend that you establish a bootable backup of your current OS on an external USB or Thunderbolt hard drive, then verify that you can boot your Mac from that backup disk. Before you pull the trigger on the upgrade, detach that external disk from your Mac and set it aside. This is a really simple step that you can do to save potentially a lot of headache in the future. And you need a backup anyway right? Make it a CCC bootable backup.

For more detailed advice on preparing for the upgrade and instructions on how to downgrade, check out this CCC knowledgebase article:

Best practices for updating your Mac's OS

When should I upgrade?

As with every major upgrade, I recommend that any users that rely heavily upon the availability of their Mac for work or other productivity consider waiting for at least one OS update before making the upgrade. The early releases are exciting, but with any excitement there's usually a bit of risk. Early adopters will surely find some shortcomings and bugs which will be resolved in the next month or so with minor OS updates. Does this upgrade fix a problem that causes me daily grief? Will this upgrade improve my productivity or security, outweighing the time I may have to invest in fixing early-adopter problems? Those are the key questions I ask myself before applying any upgrade.

What should I expect after I have upgraded? How will my backups be affected?

In most cases, you... Read More

Mike's picture by Mike | September 12, 2019


My APFS-formatted rotational disks have always felt slower than when they were HFS+ formatted. The speed of copying files to them felt about the same, but slogging through folders in the Finder was taking a lot longer. At first I shrugged it off to the filesystem being new; "It just needs some tuning, it will come along." But that performance hasn't come along, and after running some tests and collecting a lot more data, I'm convinced that Apple made a fundamental design choice in APFS that makes its performance worse than HFS+ on rotational disks. Performance starts out at a significant deficit to HFS+ (OS X Extended) and declines linearly as you add files to the volume.

The rest of this article is fairly technical, here are the key takeaways:

  • Enumerating an APFS filesystem on a traditional HDD (rotational disk) will take 3-20X longer than HFS+ on the same hardware.
  • This performance difference is most noticeable on a macOS startup disk that is (or includes) a rotational disk.
  • If Apple doesn't make some concessions in the APFS filesystem to accommodate the slower seek performance of HDD devices, then a rotational device will never be able to provide acceptable performance as a production macOS startup disk.

Test Setup

I wanted to see how an APFS formatted volume performs over time under "normal" usage conditions and how that compares to an HFS+ formatted volume under the exact same conditions. To do this, I had to set up a simulation that would produce identical changes on two volumes to allow for a consistent, objective analysis of the filesystem performance. When I refer to "filesystem performance," I'm specifically referring to how long it takes the filesystem to do transactional tasks. Read and write performance depends almost entirely on the speed of the media, so I wanted to factor that out of my tests. Enumerating the contents of the filesystem is a good exercise of filesystem transactional performance, so I decided to test the enumeration of 1 million files on each an APFS and HFS+ filesystem over a period of simulated modifications to the filesystem.

The destination device in these tests is a 2TB Western Digital MyBook Duo split into two equal partitions. One partition is formatted HFS+, the other APFS. Spotlight was disabled on both volumes. Snapshot support and APFS defragmentation were varied in different tests to determine whether they had any effect on filesystem performance.

The number of files in the file set is constant – 1 million files, 111,000 directories (files nested three directories deep). To make the simulation closer to real-life, the file size distribution roughly follows 1/x2 – it’s weighted more heavily towards smaller files. Each individual file size is determined randomly, but in a pattern that follows that size distribution histogram. Average data set size is ~18GB. Max file size is 20GB... Read More

Mike's picture by Mike | June 6, 2019

Update July 18, 2019: CCC 5.1.10-b3 is now available and addresses the bulk of the changes required for supporting macOS Catalina.

What an exciting week! Once again this year our team was graced with a WWDC "Golden Ticket". Last year I got to go, but this year Peter from our Development team went and had the opportunity to speak directly with Apple's File Systems team about the upcoming changes to APFS. Among the new announcements this year is the introduction of a read-only system volume on macOS Catalina. From the moment that Apple announced APFS, I anticipated exactly this sort of setup – user data on one volume, macOS on another – complete separation, absolute protection for the system. Apple has implemented this in a manner that will be (almost) completely transparent to the end user, and so far, I'm pretty stoked about how all of this works.

What implications does the read-only system volume have for CCC backups?

In the Finder you'll only see one volume that represents your startup disk and it will appear as if everything is on that single volume. In reality, the startup disk that you see in the Finder is the read-only system volume and doesn't have any of your data on it; the "Data" volume is separate and hidden. CCC will have to find that hidden volume (don't worry, I know where to look :-) and back up its contents alongside the system volume. The current version of CCC can't do that, of course, it knows nothing about APFS volume groups. We're adding that functionality right now, though, and we'll be hard at work over the summer on some new documentation that will help explain everything that you're seeing (or not seeing!) on the newOS.

What are the implications for my backup disk?

Allow me to be the first to say it: stick a fork in it, HFS is done. HFS simply won't work for making a backup of a Catalina system volume, so in the near future, we're going to drop support for backing up macOS (Catalina and later) to HFS+ formatted volumes. We plan to make this as easy as possible for you, though, so don't go out of your way to get ready for this. My goal is to make this transition as simple as possible for you and your backups.

If you're testing Apple's new OS already, stay tuned for another CCC beta release that will start to add support for the new features of macOS Catalina.