Can you use APFS on hard disk drive?

Can you convert a Hard Disk Drive (not SSD) to APFS?

No I would not do it at this time. 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.

You can use Disk Utility to convert external volumes from HFS+ to APFS format.

If I convert a volume to APFS, can I later revert to HFS+?

You can use Disk Utility to erase an APFS-formatted volume and reformat as HFS+. However, your data will not be preserved when you reformat the volume as HFS+.

Rotational hard drives and fusion drives were supported in Developer Preview 1, but support was removed in Developer Preview 2 ... The verbiage on this one was ambiguous. ... FYI -- in beta 13 (Sept 1) -- HDD-only Macs cannot be converted to APFS.

There is no harm in leaving your drive HFS+

If so, is it a good idea to do so?

Out of morbid curiosity I used Disk Utility to convert an encrypted Time Machine backup drive (external USB3) to AFPS. It did so without complaint and all its files appeared to be intact, but then Time Machine reported it could not be used since it was not formatted according to Time Machine's requirements (Mac OS Extended). To keep it in service as a TM backup device required that it be reformatted properly, which as you know erases everything.

So you can, but I can't think of a compelling reason to do so.

While formatted as AFPS I dragged files back and forth, copied, deleted, etc. Everything worked as expected with the usual boring predictability. It certainly did not result in any performance degradation.

Yes, external drives (including HDDs) can be converted to APFS.

They'll run faster, you'll get more storage space and it'll be more secure.

The biggest downsides as far as I can tell are:

1. The drive can only be used with High Sierra

2. The drive cannot be used with Time Machine (because APFS does not support Directory Hard Links)

I recommend backing up your hard drive before doing it. as that's always smart.

Some people say that APFS is too early to be trusted, but then again iOS has been using it for years... so it's up to you.

I don't follow your question.

High Sierra can read both APFS and HFS+ without issues. So you don't need to upgrade any drives you don't want to.

But if you are asking if it's ok to use an iMac with HFS+ with an external with APFS then yes. That works fine.

if external HHDs are able to convert to APFS, why say not do now? I have 2 HHDs for FCPX. both are still HPF+ (for now) since I would like to convert them for faster reading/ coping.

SnakeDog wrote:

... but then again iOS has been using it for years... so it's up to you.

iOS has been using APFS introduced in the iOS10.3 rollout. 😉

Right, not years... but it's been used for a while now (March 2017) by lots of iOS devices (millions?)

I'm just saying it feels like brand new, but it's been tested for a while now.

So, if HHDs are then APFS, and my iMac is the 2017 fusion drive (not able APFS), will it be “okay” to continue editing?

It is about whether the .fcpbundle library on hdd will gain speed and space.