Which file system does Apple use

APFS Explains: What You Need To Know About Apple's New File System

Apple's macOS 10.13 High Sierra brings with it a new file system called "Apple File System", which largely replaces the older HFS + file system. Apple File System, also known as APFS, has been used by default on iPhones and iPads since iOS 10.3, and also on Apple Watch and Apple TV - now it's finally available on the Mac too.

How to get the Apple file system

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You don't have to do anything special to switch Mac to the new APFS file system. Just upgrade to macOS 10.13 High Sierra. The update process will automatically migrate your Mac's internal drive from HFS + to APFS if your Mac's internal drive is an SSD or other all-flash storage device.

This process is automatic. On a Mac with full flash storage, the internal partitions are migrated from HFS + (also known as Mac OS Extended) to APFS. There is no way to disable this conversion.

Fusion drives (which are both flash and (traditional magnetic storage), traditional hard disk drives, and non-Mac volumes (such as Windows Boot Camp volumes) will not be migrated. While APFS does not currently work on Fusion Drives, Apple plans to use APFS in the future Activate Fusion Drives.

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External drives, including USB drives and SD cards, are also not migrated to APFS. You can format an external drive as APFS using Disk Utility. However, other file systems are recommended. For example, exFAT offers better compatibility with Windows and other devices. Mac OS X Extended provides compatibility with High Sierra as well as Macs running older versions of the macOS operating system.

Your Time Machine drive cannot be formatted with APFS either. Time Machine can back up from an APFS drive, but the Time Machine target drive must be formatted as HFS +. The operating system does all of this automatically. Just don't try to manually convert your Time Machine hard drive and you'll be fine.

The advantages of APFS

Why bother with APFS at all? It offers a number of advantages over HFS +, particularly performance and reliability, as well as some improvements in encryption and partitions.

Performance increases

You won't see any new features with a new filesystem, but you will see a variety of improvements under the hood. For example, some file operations have improved performance.

Perhaps the size of the directory is actually more noticeable. Clicking the Inspector button for a large folder will display the total file size of the folder noticeably earlier. This is because APFS stores file size metadata in a location that can be accessed more quickly, whereas HFS + let the operating system examine the metadata of each file in turn.

Copying files is also faster. For example, suppose you are copying a file from one folder to another. Rather than simply making a second copy of this file's data on the hard drive, APFS creates a mark stating that there are two files on the hard drive that reference the same data. This means that the copying process should be done immediately. If you change either file, APFS will save both the original and changed files and everything will work as you expect. It's just faster and more efficient under the hood.

The performance of creating "sparse files" is also improved. In other words, if an application creates a large, empty file, it is now much faster. With HFS +, an application creating a 5 GB file would have to wait while the operating system writes 5 GB zeros to the hard drive. With APFS, the file system marks the space as allocated but does not write to it immediately. Therefore, it should now happen almost instantly.

Reliability and data integrity improvements

Apple's new file system is also more resilient to data corruption due to errors and power outages.

APFS uses "copy-on-write". For example, if you update a file's metadata; For example, the file name, the HFS + file system changes this metadata directly. If your Mac crashes before the process is complete, data can become corrupted. If you use APFS to change the metadata of a file, APFS creates a new copy of the metadata. APFS does not refer the original file to this metadata until the new metadata has been written. Therefore, there is no risk of the metadata being corrupted. This feature is also found in other modern file systems such as ZFS and BtrFS on Linux and ReFS on Windows.

The Apple file system also uses what is known as Atomic Safe-Save, which is like copying-while-writing, but applied to other file operations, including renaming or moving a file.

Reliability is also improved thanks to APFScreating and storing checksums for data on the hard drive. When APFS writes a file to disk, it examines the file, runs it through a mathematical formula that generates a shorter string that matches the file, and writes that to disk as well. When APFS reads data, it compares the data with the checksum on the hard drive and verifies that it matches. If the data does not match the checksum on the hard drive, this indicates data corruption. This could be due to a bug, a hardware failure, or something else. However, the operating system can recognize this immediately.

Other new features

This file system also forms the basis for new features and other improvements that can build on the APFS offerings.

For example, APFS contains snapshots at the file system level. The first snapshot contains a full picture of the entire drive, while future snapshots contain only the changes made since the previous snapshot. Only new data that you have added takes up space. Time Machine works similarly, but APFS's snapshots are even more efficient. Time Machine doesn't use APFS yet, but Apple may switch Time Machine to APFS from macOS in a future version.

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APFS also supports multiple key encryption, which allows different keys to encrypt different data on the hard drive. How FileVault encryption works has not changed yet. However, one day macOS could use different encryption passphrases for each user's data and system data.

"Space sharing" is a new feature that some people will benefit from today. If you created multiple volumes (partitions) on a physical disk, you had to decide in advance how much space each volume would get. So you can create five different 100 GB volumes on a 500 GB drive. If any of these volumes require more than 100 GB of storage space, you will need to resize the volumes manually. However, if a volume only takes up 20 GB of space, 80 GB of space is wasted unless you resize the volume and then reassigned that space to another volume. With APFS, you can create five volumes on a 500GB drive without worrying about how much each one takes. The volumes share the storage space. As long as the total space used by these five volumes is less than 500 GB of total available space, things just work.

For more technical information on APFS, see the Apple developer website.

What do I need to know about using APFS?

The switch to APFS should be largely transparent. Your drive will be migrated automatically if APFS supports it. Time Machine and File Vault continue to function normally.

There are a few issues with Boot Camp, however. A Windows system installed alongside macOS cannot yet read APFS even with Apple's Boot Camp software installed. This means that you cannot currently change the startup disk through the Boot Camp Control Panel in Windows. To restart MacOS, hold down the Option key while starting your PC and choose MacOS. You can still control your startup disk through System Preferences> Startup Disk in macOS. Hopefully Apple will fix this soon.

When using Disk Utility (available from Finder> Applications> Utilities> Disk Utility). You'll likely find that your Mac's drive is APFS (unless it's a Fusion drive or a mechanical hard drive that hasn't been migrated).

Thanks to space sharing, even if you have a single disk (partition) on your drive.Like most other disks, your drive is formatted with an APFS container that can hold multiple disks. Because of this, you will find that it is shared by multiple volumes here.

To add a new volume, click the "New Volume" button. This will add new volumes to the larger APFS container. They appear like normal volumes or partitions in Finder and elsewhere on the system, but they share space with all other volumes in the APFS container.

Do not use the Partition button to add a new partition unless you want to add a new non-APFS volume to your system. Adding a new partition will consume space for the APFS container. However, this is mandatory if, for example, you are adding a Windows volume for Boot Camp.

You still have some control over the size of your APFS volume. When creating a new APFS volume, you can click the Size Options button and specify a reserve (minimum) size and quota (maximum) size for the volume to ensure it doesn't get too small or too big. Of course, this is not necessary. APFS will work automatically even if you don't specify these options. They only exist when you want that extra control.

Switching to APFS will go unnoticed by most Mac users, but it lays the groundwork for future improvements, boosts performance in certain situations, and protects against data corruption. In addition, macOS will be moved to the same file system that is already used by Apple's other iOS operating system.