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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?

  • 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

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.

  • 2
    I 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
  • 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 (eclecticlight.co/2017/07/24/…) – LangLangC Sep 28 '17 at 17:31
  • @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." (support.apple.com/en-us/HT208018) – oa- Sep 28 '17 at 17:59

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