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Mike's picture by Mike | March 30, 2018

On the eve of World Backup Day and with stories like the Atlanta ransomware attack still in the news, now is a great time to revisit your backup strategy. It's also a great time for us to announce some great new features that we're getting ready to deliver as a free update to CCC 5 users – features that will help you improve your defenses against ransomware and malware.

Versioned backups with APFS Snapshots

CCC 5.1 offers support for point-in-time restores by leveraging the snapshot feature of Apple's new APFS filesystem. CCC's SafetyNet feature offered similar functionality to this in the past, but snapshots take it to a new level, allowing you to do things like restore a previous version of the OS and older versions of your Photos library.

CCC is also the first comprehensive snapshot management utility for macOS. Browsing the contents of any snapshot is just a click away, and should you want to delete a specific snapshot (whether created by CCC or Time Machine), just select it and press the Delete key. How much space are those snapshots consuming? CCC can tell you that. No other utility offers this much insight into your APFS volumes' snapshots!

CCC 5.1 introduces comprehensive support for APFS snapshots

CCC 5.1 is currently available for beta testing. If you're the beta-software-testing type, check the "Inform me of beta updates" box in the Software Update section of CCC's Preferences window, then click the "Check for updates now" button if you would like to try it out.

Learn more about how you can add snapshot support to your backup strategy

Read-only snapshots offer great protection against ransomware

Snapshots are read-only copies of your volume. Not only is it impossible to modify the content of those snapshots, but it’s also not possible to delete those snapshots without a special entitlement granted by Apple. What that means is that malware and ransomware can't delete your snapshots. So if you were somehow affected by ransomware and it started encrypting your files, you could remove the ransomware, then restore your files from the snapshot. CCC backups could literally save you thousands of dollars!

What can I do to make sure my backup strategy is going to be effective?

I have four general tips: make backups to a locally-attached hard drive, keep it current, keep it encrypted, keep it unmounted.

Make backups to a locally-attached hard drive

NAS backups sound convenient and Cloud backup is the buzz, but when it comes down to actually using your... Read More

Mike's picture by Mike | February 15, 2018

Update March 30, 2018: This issue persists on macOS 10.13.4 (17E199)


This week we reported to Apple a serious flaw in macOS that can lead to data loss when using an APFS-formatted disk image. Until Apple issues a macOS update that resolves this problem, we're dropping support for APFS-formatted disk images.

Note: What I describe below applies to APFS sparse disk images only — ordinary APFS volumes (e.g. your SSD startup disk) are not affected by this problem. While the underlying problem here is very serious, this is not likely to be a widespread problem, and will be most applicable to a small subset of backups. Disk images are not used for most backup task activity, they are generally only applicable when making backups to network volumes. If you make backups to network volumes, read on to learn more.


Disk images are handy devices. They're files, but they act like a hard drive – you mount a disk image by double-clicking the file, then it behaves like it's another hard drive attached to your Mac. macOS has been using disk images for decades, and we find them particularly useful when making backups to network volumes. By formatting the disk image volume using an Apple-native format, we can do things like back up system files.

Naturally, when Apple introduced APFS in macOS High Sierra, we sought to offer support for using APFS on destination disk images when doing so would match the format of the source volume. As far as creating and mounting disk images is concerned, APFS and HFS+ are easily interchangeable, so adding support for APFS was very straightforward. Unnoticed by us, Apple, and thousands of developers, however, is a very subtle behavioral difference that is specific to APFS on a sparse disk image.

Earlier this week I noticed that an APFS-formatted sparsebundle disk image volume showed ample free space, despite that the underlying disk was completely full. Curious, I copied a video file to the disk image volume to see what would happen. The whole file copied without error! I opened the file, verified that the video played back start to finish, checksummed the file – as far as I could tell, the file was intact and whole on the disk image. When I unmounted and remounted the disk image, however, the video was corrupted. If you've ever lost data, you know the kick-in-the-gut feeling that would have ensued. Thankfully, I was just running some tests and the file that disappeared was just test data. Taking a closer look, I discovered two bugs in macOS's "diskimages-helper" service that lead to this result.

An APFS volume's free space doesn't reflect a smaller amount of free space on the underlying disk

In the past with HFS+ formatted disk images, the disk image volume would automatically adjust its free space to accommodate any differences between the disk image volume's capacity and the... Read More

Mike's picture by Mike | October 19, 2017

Well, I did it. I know that I've told many people I'd be waiting until Thanksgiving to apply the High Sierra upgrade to my own production machine, but after some reflection this week, I decided that High Sierra was ready for me, and that I was ready for High Sierra. I've always been decidedly anti-upgrade when it comes to my own production system. Upgrades tend to break things, and I just can't afford downtime on my laptop. High Sierra and the APFS transition, to me, was a potential double-whammy for breaking things, so I was bearish on this upgrade in particular. But today, we're ready.

I didn't make this decision lightly. The scientist in me kicked into gear and I started analyzing some data. I looked at new OS adoption among our user base, I looked at our Help Desk analytics, and I considered the experiences of the users that I've been helping over the past several weeks. As I predicted early in the summer, the APFS conversions have largely gone just fine. This is probably at least partially attributable to Apple backing off on applying the new format to Fusion and AppleRAID devices, but I think some credit to Apple is due here. They pulled this off! The upgrade hasn't been flawless, but based on the feedback that we've received from our users, largely it has gone fine, and anecdotally I think it has gone better than past OS upgrades.

OS adoption among CCC 4 and CCC 5 users

Looking at just the last week, I can see that approximately a quarter of CCC users have upgraded to High Sierra. Sierra remains the dominant OS choice, but I think we'll see that flip in the next three to four weeks; perhaps once the 10.13.1 release is posted.

OS Adoption among CCC 4 and CCC 5 users, second week of October

CCC rises to the APFS challenge

So how did CCC do with the upgrade? In the 16-year history of Mac OS X, High Sierra was the first OS upgrade to introduce a new, bootable filesystem format, so obviously that posed a challenge to the bootable backup solution. In just four months, we picked apart the boot semantics of this new filesystem, added format-agnostic support to CCC 5, tested dozens of source/destination filesystem combinations, assembled numerous pages of support documentation and several new Help videos – CCC was ready for APFS when High Sierra shipped on September 25.

I don't want to be the guy that hoists a "Mission Accomplished" banner too early, but looking back at the last several weeks, we were more prepared for this OS release than any major new OS in the past. We've seen great success making HFS and APFS bootable backups on High Sierra. Our statistics show thousands of confirmed High Sierra bootable backups using both APFS and HFS (roughly 40/60 split), and based on user feedback on our... Read More

Mike's picture by Mike | September 29, 2017

One of our users made a startling discovery this week after upgrading to High Sierra. He had an HFS+ formatted 16TB RAID device, and had always intended to enable encryption on that volume. There's no OS on it, so he simply right-clicked on the volume in the Finder and chose the option to encrypt it:

Screenshot of Finder contextual menu showing encryption option

This is an easy way to enable encryption on a volume: plug in a password, verify, add a hint, done!

Prompt for encryption password

Oddly, though, CCC, Disk Utility, and Terminal all agreed that his HFS+ volume was now an APFS Encrypted volume. Naturally he contacted AppleCare. "Not possible, says Apple", he reported.

It is apparently possible, however, and I was able to confirm this behavior on my test system. Take any HFS+ formatted volume that does not have an installation of macOS on it (that part is key), right-click on the volume in the Finder and choose the option to encrypt it. Rather than simply converting the volume to a CoreStorage Encrypted volume and keeping the HFS+ format, macOS converts the volume to APFS with no warning, and then enables encryption.

Potential hazards of converting your data volumes to APFS

Apple has demonstrated that the conversion from HFS+ to APFS has gone pretty smoothly, but there are a few scenarios where you might want to give some serious thought to that kind of conversion.

Did I want my expensive RAID device to be my APFS Guinea Pig?

APFS is supported atop RAID devices, so this conversion will surely work out just fine. That's what I'd be telling myself had this happened to me, but I'd certainly have appreciated some warning. Deciding to turn on encryption has one set of implications, and we've had our hands on HFS+ CoreStorage encryption since OS X Lion, so there aren't many surprises left. Adding a filesystem format change might make me decide that this is a bit too risky for this particular device. What if there's a specific issue with my vendor's RAID? Wouldn't I at least like the opportunity to reach out to that vendor for comment before casually flipping this irreversible switch?

APFS Encrypted volumes are not backwards-compatible

Do you share your disk between Macs? APFS Encrypted volumes aren't backwards compatible at all, so if you attach that converted disk to a Mac running an older version of the OS, you're greeted with this heart-attack-inducing error message:

The disk you inserted was not readable by this computer

I'm using the term "older Mac" fairly loosely, this... Read More

Mike's picture by Mike | September 26, 2017

The time for betas is over! High Sierra is here. APFS is here. We're ready for both, and we've got you covered. APFS, HFS, encrypted, not encrypted, FileVault – whatever your source or destination, we support all of these combinations in CCC 5. We've tested so many different scenarios, we put the results into a chart to keep track of them.

"Can I continue to back up to an HFS+ volume, or do I have to erase the backup disk as APFS?"

Over the last day or so, we've been getting this question a lot from folks that have upgraded to High Sierra. This new filesystem has generated so much confusion, we even got the question, "Can I still back up to an HD platter-based disk?" We expected some concern about what's supported on each end, but the lack of support and readiness for all of these combinations from other products is causing even more confusion than we anticipated.

My answer is that all of these configurations work with CCC 5, and that you don't have to change how your destination is formatted. CCC 5 automatically archives the special boot volumes associated with an APFS source, and automatically populates them, as necessary, if you have an APFS destination (even if the source is HFS!). We specifically tested all of these scenarios and set up a "command central" for our testing and for reporting issues that we're seeing that are specific to macOS High Sierra:

High Sierra Testing and Known Issues

I hope that chart goes a long way toward relieving concerns about what is an acceptable source and destination format for your High Sierra backups. But just to reiterate:

  • CCC can clone your High Sierra SSD to an SSD or an HDD that is formatted as either HFS or APFS.
  • CCC can restore an HFS-formatted High Sierra backup to an APFS or HFS volume.
  • CCC can make bootable APFS backups.
  • CCC can make bootable HFS backups.
  • You can mix and match APFS and HFS sources and destinations – CCC will make the destination bootable.

CCC handles the special APFS "helper" volumes seamlessly, and quietly

Only CCC has supported Recovery HD archiving and cloning since Apple introduced that special volume in OS X Lion five years ago. The semantics for creating and populating those volumes are a bit different for APFS, but these special APFS helper volumes are very similar to the HFS Recovery HD volume. As a result, our intellectual and technical investment that we made in recovery volume support over the last five years has paid off. We were able to add support for APFS helper volume archiving and creation fairly quickly, and we spent the bulk of... Read More