Here’s a brief guide to the different file systems supported by the first release of High Sierra 10.13 on different types of disk.
Solid state (SSD, excluding Flash):
- Internal – converted to APFS when High Sierra is installed on them, no option. Left unconverted if High Sierra installed on external drive. Can be converted from HFS+ Journaled to APFS, and formatted as APFS, using Disk Utility in High Sierra.
- External – not converted when High Sierra is installed on them from Sierra, no option, and installer will not install from Sierra onto APFS, only HFS+ Journaled. When High Sierra is installed on them from High Sierra, though, it will install onto APFS if so formatted, but does not automatically convert.
- CoreStorage – if an SSD is part of a CoreStorage ‘fusion’ drive, even if the other drives are also SSDs, then it will be left in HFS+ and cannot be formatted as APFS. If you want to convert it to APFS, you must defuse it by uninstalling CoreStorage and turning the SSDs back into separate drives again.
Flash (including USB memory sticks):
Some cannot be converted to, or formatted in, APFS. Disk Utility (High Sierra) either does not offer the option, or returns an error when attempted. Others can be, at least in Disk Utility, but this must be performed using the Partition tool, not Erase. Behaviour appears inconsistent, and can also result in errors when formatting or in use.
Fusion Drives (combined SSD and hard disk, united in CoreStorage):
- Cannot currently be converted to APFS. Unsupported for APFS in this release. Problems were experienced during beta testing, so do not try.
- Home-brew ‘fusion drives’ could be defused into separate SSD and hard disks, then the SSD formatted in APFS, if you wish.
Hard disks (rotating):
Cannot currently be converted to APFS. Unsupported for APFS in this release. Problems were experienced during beta testing, so do not try.
File transfer HFS+ <-> APFS:
- under High Sierra – fully supported and appears reliable.
- under Sierra – unsupported and prone to error and problems. Avoid if possible, using HFS+ or iCloud Drive as an intermediate store.
If you experience difficulty getting Disk Utility (High Sierra) to format a disk in APFS, select the drive at the left, then click on the Partition tool above, and select the APFS option if offered. You can then add additional volumes, if required, by selecting the drive at the left and using the Volume tool above the list of drives.
Unless you know exactly what you are doing, you should only use the APFS or APFS (Encrypted) options. Using the case-sensitive version is likely to cause many issues. Note that APFS encrypted volumes are completely unusable in Sierra 10.12.6; unencrypted volumes work much of the time, with only occasional errors and problems.
Other possibilities may be available using command tools. If you have any different experiences, please let us know in a comment.
(Updated 5 October 2017.)