I've got a few USB 3.0 HDDs I use for backup and game storage, all formatted in HFS+.
What are the advantages/disadvantages of migrating to APFS on an HDD?
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I suppose this might depend on what steps you take to migrate an HDD to APFS. Do you have a specific macOS version and procedure in mind? – bmike Sep 28 '17 at 10:59
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APFS (Apple File System) compared to HFS+
Almost all differences apply to Solid State Drives (SSD) and Hard Disk Drives (HDD) as well, while users of HDDs may not see an improvement in speed.
APFS disadvantages/drawbacks
- Incompatible with macOS 10.12 Sierra and earlier (including OS X)
- Windows drivers/tools to read/write APFS disks are not available (as of today)
- Currently not supported by Fusion Drives/HDDs (coming soon)
- Boot Camp doesn't read from or write to APFS-formatted volumes
- No AFP support: Volumes formatted as APFS can't offer share points over the network using AFP.
- Any Time Machine share points must be shared over SMB instead of AFP.
- Directory Hard links are not supported
- File names cannot contain unassigned codepoints in the Unicode 9.0 standard
APFS advantages
- Faster disk speed in general on SSDs
- Almost instant file and directory duplication
- Increased maximum number of files
- Space sharing
- Better crash protection
- Better date resolution: nanosecond timestamps
- Support for dates beyond February 6, 2040
- Sparse file support
- Larger max. number of files (2^63 vs 2^32)
- Supports Copy-on-Write (replaces journaling)
See also Apple's APFS Developer Guide and the Wikipedia's Apple_File_System.
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2I think the bit about hard links is not entirely correct: as far as I know, APFS does not support directory hard links, but it does support regular file hard links. – Rinzwind Sep 28 '17 at 15:38
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Hm, isn't APFS completely unsupported on OS X but with limited support on macOS up until 10.12.5 – except being the boot volume for 10.12? 10.12.6 then breaking some stuff (https://eclecticlight.co/2017/07/24/sierra-isnt-finished-yet-apfs-support-is-undone-in-10-12-6/) – LаngLаngС Sep 28 '17 at 17:31
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1@LangLangC At least not officially: "For example, a USB storage device formatted as APFS can be read by a Mac using High Sierra, but not by a Mac using Sierra or earlier." (https://support.apple.com/en-us/HT208018) – oa- Sep 28 '17 at 17:59
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2According to https://bombich.com/blog/2019/09/12/analysis-apfs-enumeration-performance-on-rotational-hard-drives, it seems that "Enumerating an APFS filesystem on a traditional HDD (rotational disk) will take 3-20X longer than HFS+ on the same hardware." – He Yifei 何一非 Jul 19 '20 at 23:02