Yesterday’s article about selecting hard disks raised questions about whether APFS is now officially supported on them. Although I stated that it is not, that is neither completely correct, nor competely wrong. This article tries to clarify APFS support beyond SSDs.
APFS has worked on non-SSD storage since May-June 2017. In his presentation to WWDC in June 2017, Pavel Sokolov, a File System Manager, stated unequivocally that APFS was the official replacement for HFS+, Fusion Drives were fully supported as boot volumes, APFS stored all its metadata on the SSD part of a Fusion Drive, APFS automatically defragments on hard disks, hard disks were not automatically converted from HFS+ to APFS during High Sierra installation, and performance improvements were still being sought.
There was no doubt at that time that APFS was intended to replace HFS+ as the standard file system across hard disks, Fusion Drives, and SSDs.
However, when High Sierra 10.13 was released on 25 September 2017, not only did it not convert Fusion Drives to APFS, but Apple made it clear that APFS was not then supported on Fusion Drives. There were reports at the time that Apple staff stated that such support would be provided in a future update to High Sierra, but I did not see any written release from Apple making that clear, nor was there any promised timescale.
APFS has been updated several times since 25 September, the last being in the 10.13.3 update of 23 January 2018. I have not come across any release notes which have claimed any change in the storage supported by APFS. However, on 5 February 2018, Apple updated its developer documentation to state that:
Apple File System is optimized for Flash/SSD storage, but can also be used with traditional hard disk drives (HDD) and external, direct-attached storage. and
Can I boot macOS High Sierra from an APFS-formatted hard disk?
Yes. macOS High Sierra supports Apple File System for both bootable and data volumes.
No mention is now made of Fusion Drives in that FAQ.
There are other Apple support documents which cover APFS for users. Among them, this article provides advice on choosing the most appropriate format for disks. It states that the installation of High Sierra results in the automatic conversion of SSDs to APFS, and that Fusion Drives and hard disks aren’t converted. It gives no advice as to which to choose when formatting a hard disk, although it hints heavily that APFS is intended mainly for SSDs.
Help for High Sierra’s Disk Utility mirrors the developer FAQ, advising that
While APFS is optimized for the Flash/SSD storage used in recent Mac computers, it can also be used with older systems with traditional hard disk drives (HDD) and external, direct-attached storage.
It does not mention Fusion Drives.
So, as of High Sierra 10.13.3, APFS is the standard file system for SSDs which are only used by High Sierra systems, “can” be used on hard disks which are only used by High Sierra systems, but remains unsupported on Fusion Drives.
There are four major limitations to the use of APFS.
Time Machine backup drives cannot be in APFS format, but must either be in Journalled HFS+, or networked via SMB. As far as I can tell, Apple has given no indication as to whether the current version of Time Machine will ever support APFS, or what its solution will eventually be. Whatever the type of drive, if it is to be used for Time Machine backups, it must be in HFS+ format for the foreseeable future.
Shared storage is an interesting case. At present, AFP is deprecated but still works for drives which are not formatted in APFS. Networked drives which are formatted in APFS are not accessible by AFP, though, and can only be accessed using SMB or NFS. They cannot be used for Time Machine backups anyway.
If you prefer a volume cloning and backup tool, then SuperDuper! version 3.1.4 claims full support for APFS, as does Carbon Copy Cloner 5. Both should work fully with non-SSD APFS drives.
AppleRAID doesn’t support APFS, although Apple claims that you can combine APFS volumes with Apple RAID volumes to support RAID levels 0 and 1. For most RAID users, that is woefully inadequate. SoftRAID will support APFS in version 6.0, which is currently in test. So at present there is essentially no support for software RAID on APFS volumes.
Access from Sierra
Although macOS Sierra’s APFS support was updated in the recent security update, you shouldn’t ever expect a Sierra system to be able to mount and access an APFS volume. APFS support in Sierra was only ever pre-beta, and that in High Sierra has continued to diverge ever since its release. You may be lucky enough to get an unencrypted APFS disk to mount on a Sierra system, and may even get some files off it, but Sierra currently cannot even see an encrypted APFS volume, let alone try to access it.
One potentially good reason for wanting to use APFS for an external disk is its superior encryption. Because APFS encrypted volumes cannot be accessed from Sierra, you should only consider using them in situations where there will never be any need to attempt that.
Repair and data recovery
Bundled Disk Utility in High Sierra has full support for APFS, with supporting tools such as
Support from third-party tools remains more patchy. For example, DiskWarrior 5.0 does not support any operations on APFS, but Prosoft claims its Drive Genius supports all features apart from defragmentation and repartitioning of APFS containers/volumes. iBoysoft Data Recovery for Mac is claimed to work fully with APFS, and the same team in Chengdu, China, has implemented APFS support for Windows. I don’t know how well either works, and welcome your experiences, please.
If you were to send your damaged 16 TB APFS drive off to a data recovery centre today, they would probably not get results comparable to those from a damaged HFS+ disk. It may be many more months before their service for APFS matches that currently achieved with HFS+ recoveries.
So yes, it appears that APFS is now supported on hard disks, provided that you don’t want to use them to store Time Machine backups, don’t use them in a RAID array, don’t need to access them from Sierra, and won’t need to recover data from them in the event of damage. You may also find that they performed better when formatted in HFS+, which seems to be the consensus from experience.
As for Fusion Drives, which I fancy far outnumber internal hard disks in relatively recent Macs, the answer still seems to be no, across the board.
I have now located a clear and very official statement that macOS High Sierra 10.13 didn’t support Fusion Drives or hard disks – in the launch press release of 25 September 2017:
APFS currently supports every Mac with all‑flash internal storage — support for Fusion and HDD Mac systems will be available in a future update.
There has been no more recent press release which has updated that statement.