#PSA: APFS Is Going To Be The Default Filesystem In High Sierra If You Have An SSD

If you are planning to upgrade to macOS High Sierra when it ships in September, I would strongly suggest that you make a backup before upgrading. Now to be frank, you should do that anyway as you need to be able to cover yourself in case an OS upgrade goes south. But this time it’s doubly important. A support document was just posted to the Apple Support site and it says the following:

Apple File System (APFS), is the default file system in macOS High Sierra for Mac computers with all flash storage. APFS features strong encryption, space sharing, snapshots, fast directory sizing, and improved file system fundamentals.

When you upgrade to macOS High Sierra, systems with all flash storage configurations are converted automatically. Systems with hard disk drives (HDD) and Fusion drives won’t be converted to APFS. You can’t opt-out of the transition to APFS.

The document is here: https://support.apple.com/en-us/HT208018

The fact that anything with an SSD will get converted to APFS and you cannot do anything to stop could be scary. Here’s a few reasons why:

  • The drive may be inaccessible by other file systems.
  • If the OS breaks down for some reason, this may make recovery of data a serious issue. Third party disk utility DiskWarrior for example does not currently have APFS support. Other similar utilities are in the same boat.
  • What if you have some piece of software that doesn’t play nice with APFS? Well, you’ll likely find out after you install High Sierra and you’ll have to roll back to the Sierra OS if you have a backup.
  • What if you have a non-Apple SSD in your Mac? Will that be converted? This document doesn’t answer that question. If it does get converted, will it run into issues as I am sure that Apple can’t test every SSD variant out there.

Now, here’s a few reasons why this may be a non issue:

  • APFS is faster
  • APFS gives more accurate time stamping of files
  • APFS allows concurrent access, while the present filesystem HFS+ has central locks, which ends up being a massive performance improvement on very multicore machines, since they’re not constantly sat in spin-locks waiting on IO
  • APFS supports snapshotting and copy on write
  • APFS supports sparse files
  • APFS’s implementation of hard links actually works
  • APFS has decent, not-hacked-in support for TRIM
  • APFS encryption is more secure
  • APFS can quickly compute the size of the contents of a directory
  • APFS can do write coalescing
  • APFS uses volumes, rather than partitions, letting them be dynamically resized

But the biggest reason is that if you’re running any version of iOS 10.3 since March of this year, you’re already running APFS on your iDevice(s) and as far as I know, there hasn’t been any problems with it. Thus moving a bunch of Macs over to APFS may be a non-event.

My advice is going to be the same one that I started out this article with. If you plan on moving to macOS High Sierra, make sure you have a backup just in case things go sideways. It’s the best way to protect yourself.

2 Responses to “#PSA: APFS Is Going To Be The Default Filesystem In High Sierra If You Have An SSD”

  1. […] Upgrade… At least not yet: macOS High Sierra brings a brand new file system called APFS to the table as well as the fact that Microsoft has warned that Office may not work with High Sierra. […]

  2. […] Fusion Drives and spinning disks will be coming at some point in the future). And as I have noted previously, you’re going to get this new filesystem on your SSD whether you want it or not. Apple also […]

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