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New macOS, New Filesystem: What Is APFS and How Does It Work?

Michael McConnell 16-08-2017

When High Sierra releases this fall, Mac users will get the option to convert their drives to the new Apple File System (or APFS). If you are an iOS user, you have already been using it since 10.3 Apple IDs, AirPods, and APFS: What's New in iOS 10.3? Apple ID management, AirPods support, and the debut of APFS -- wondering what all of that means? Let's take a closer look at iOS 10.3. Read More .


Developers have been able to make non-bootable drives for some time now, but converting your entire system drive is a big decision. What exactly are we getting into this fall?

Pour One Out for HFS+

HFS dates back to the original Mac When Did Apple Become Popular? A Brief History of the Rise of Apple How did Apple start and when did Apple become popular? We answer these questions and more in a brief history of Apple. Read More , running from Floppy Drives. It had a long life. You could read HFS drives until Snow Leopard. HFS+ (referred to by Disk Utility as Mac OS Extended) dates back to Mac OS 8.1. It had quite a few upgrades in its lifetime.

Apple bolted on compression, versioning, tagging, and encryption after its release. Taking something that ran on the original iMac and running it on iPhones and Watches probably led to interesting challenges.

Core Storage is not a file system From FAT To NTFS To ZFS: File Systems Demystified Different hard drives and operating systems may use different file systems. Here's what that means and what you need to know. Read More , but it is the reason the conversion to APFS is less painful. Core Storage is a Logical Volume Manager. It enabled Fusion Drives to swap your active and archival data between flash and spinning disk. However, it also meant that there was a layer between your data and the physical disk.

In some ways, APFS is the next evolutionary step. The file addressing moves to 64-bit, which is an exponential growth in the number of files you Mac can handle. Like Core Storage, APFS has some abstraction of the disk. Different file systems can exist in the same space of a drive.


This means you do not have to divide your drive three different ways to have three partitions. Instead, they can all use all the available space on a drive. Apple also promises reduced latency when dealing with your drive. In other ways, APFS is radically different.

Same Data, Different Files

The most immediate benefit that you will get when moving to APFS is saving a ton of space. This is because APFS handles multiple copies of the same file much differently than HFS+. When you copy a file, APFS creates a new entry in the file system that points to the same bits as the original file. This is not a shortcut — to the Operating System and Applications, they are separate files.

APFS handles changes differently. Each change you make to a file saves in a separate location from the original file. This process is a native way to support versioning as well. It also means that your original file is still only the single original bits. So is the copy that you made. On your day to day drive, this may not save much space. That may be different if you have files that change frequently.

Where APFS’s space-saving features are going to help you out is with Time Machine. We have all hit that point where Time Machine warns you that your back drive is out of space. Your only option at that point is to either move your backup to a new drive or let Time Machine roll off your oldest backups.


Snapshots and Backups

Beyond saving space by changing the way macOS makes copies, backups can be different as well. When backing up the filesystem, APFS will use what are called Snapshots. This makes a read-only version of the filesystem in place, allowing you to revert at any time. These are already commonly used in enterprise IT back up systems.

It is not clear if that will change the way that Time Machine backs up your files. Time Machine takes these between your connections to your backup drive. The file system can essentially create restore points. You can step back to them to erasing all changes in the interim. This is an attractive feature that might make significant differences in the way macOS backs up.

Encryption and Double Secret Encryption

After some initial issues, FileVault became a great way to protect your files on a Mac What Is FileVault on macOS and How Do I Use It? Here's what you need to know about the FileVault disk encryption feature on your Mac and how to enable and disable FileVault. Read More . APFS supports whole drive encryption as well. You can set up a key and encrypt your entire disk. This is excellent protection if someone steals your Mac since they cannot unlock your data without your password.

However, that means all of your data is available when you are signed-in. This can be an issue if you have a shared Mac. If someone uses your signed in user-account, they have access to everything. APFS allows you to create another encrypted area of the drive. Setting it up requires a second key and password to access this subset of your data.


Moving to APFS

When High Sierra comes out this fall (you can get the public beta right now How to Try macOS High Sierra Right Now Before Everyone Else macOS High Sierra is now available for beta testing. If you'd like to give it a try before the general release, here's how to get your hands on it now. Read More ), you have an option to update your drive to APFS. If you choose this option, your drive converts as part of the upgrade process. This was rather painless in the iOS upgrade process, so there should not be much to worry you. Before you upgrade, you should make sure you have a good backup (possibly even a bootable clone), just in case.

add apfs volume macos high sierra

You can convert your HFS+ drive to APFS without losing data, but the return trip is not as smooth. If you want to switch your drive back to HFS+, you have to format your drive and reinstall. A clone would allow you just to overwrite the drive, rather than a lengthy Time Machine restore.

New OS Season Is the Best Season

Even if you do not spring for new hardware, Fall always means something new for Apple users. High Sierra is not bringing a ton of new features to macOS but for nerds, APFS is probably one of the most exciting.


The space saving aspects of the file system are going to be a significant benefit on modern Macs with smaller SSDs. However, if you rely on third party disk tools Carbon Copy Cloner - A Free & Powerful Backup Utility (Mac) Read More , you may want to hold off until they support APFS. As for Apple, it would be good to get some details on their tools. The details are particularly important for major apps like Time Machine.

What is your favorite feature of High Sierra? Are you moving to APFS right away? If you are waiting, what is your reason? Let us know in the comments.

Related topics: APFS, File System, macOS High Sierra.

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  1. Nicolas
    August 23, 2017 at 8:33 am

    Not much to do or think about until it's supported by the open source community. Until then, it's just another great idea that restricts us to a single platform. No thanks, been there, never going back.

    Come on Apple, this is 2017, not the Microsoft 90's. I left Microsoft because of this closed-source environment stranglehold. I expected you to continue bridging across platforms as you did last decade, not replicating the restrictive MS strategy.

  2. d3Xt3r
    August 17, 2017 at 8:31 pm

    Any word on if APFS supports disk-wide transparent compression, like NTFS or btrfs? While HFS+ supports compression, it's less than user-friendly and not really designed to compress entire filesystems. Having a compressed filesystem will be immensely useful for smaller storage drives.

    • Michael
      August 18, 2017 at 8:22 pm

      From what I found in my research it isn't currently supported. That isn't to say that it won't be added later.