I have a 2017 5K iMac running Mojave 10.14.6. It has a 2 TB Fusion drive internally formatted as HFS+. FileVault is not enabled, but I wish to do so. Will the disk have its format changed to APFS if I enable FileVault?

My recollection is that the disk was originally formatted as HFS+ from the factory and when I turned on FileVault, the format changed to APFS. Granted that was over a year ago, so I could be very off-base.

I want to prevent going to APFS again. The performance degraded to dismal levels. Now that I have reformatted as HFS+, it is surprisingly speedy.

  • The conversion usually happens with an OS update, not with turning FileVault on. However, APFS has improved performance on mechanical drives.
    – benwiggy
    Sep 9, 2020 at 21:36
  • @benwiggy I want to prevent APFS at all costs. I have seen a ten-fold increase in speed since dumping APFS.
    – Paul Waldo
    Sep 9, 2020 at 22:18
  • I mean APFS has been improved to work better on hard drives since it first came out. It you refuse, then you won't be able to upgrade the OS to Catalina or beyond.
    – benwiggy
    Sep 10, 2020 at 7:06
  • Thanks for the warning @benwiggy. I had no idea APFS was required for Catalina. That stinks!
    – Paul Waldo
    Sep 10, 2020 at 14:16
  • I thought Mojave was required to be installed on a APFS volume? Sep 10, 2020 at 15:40

1 Answer 1


FileVault and APFS are two very different things; enabling one doesn’t enable (or necessitate) enabling the other.

FileVault is encryption - it scrambles, to put it simply - the contents of your drive with a known key. Specifically, it uses a 128-bit AES encryption with a 256-bit key. See Use FileVault to encrypt the startup Disk for additional details. You can encrypt journaled HFS+ (JHFS+) formatted volumes as well as APFS volumes.

APFS (Apple File System) is simply Apple’s next generation file system. As far as encryption goes, it supports it natively unlike JHFS+.

  • That is what I thought @Allan. I was looking for confirmation.
    – Paul Waldo
    Sep 10, 2020 at 14:10

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