External HDD converts to APFS when encryption enabled.

[400]

New 6TB, part of back up etc etc. Format as I would for my other external hard drives, all spinners. Enable encryption and disk convert to APFS.

Have I missed something?

iMac 2013 on 10.13.6 public beta.

 

[treekram]

This indeed happens - I tried it (10.13.6). It's also been noted by the CCC folks:
https://bombich.com/blog/2017/09/29/think-twice-before-encrypting-your-hfs-volumes-on-high-sierra

So your option, should you want to encrypt a HFS+ disk in High Sierra is either to encrypt when you first erase (format) the disk using Disk Utility or to use the Terminal app to use the diskutil command (if you already have data you want to keep, you have to use this).
https://derflounder.wordpress.com/2012/01/06/encrypting-10-7-non-boot-volumes-without-erasing-them/

 

[redpandadev]

Yup, virtually any time you turn encryption on, the disk will be converted to apfs. I filed this as a bug starting back with the 10.13 betas. It was closed and marked "works as expected." I followed up with a feature request suggesting that it should prompt the user before conversion, giving them a chance to cancel if the conversion is not consistent with their expectation. That one has been open and remains open in the latest Mojave betas.

 

[400]

Thank you both. Diskutil and reformatted with the encrypt option and issue filed with Apple. I assume the the issues for spinning disks still exist. Not sure when I added my last HD but it did not do this, 10 months ago?

Anyway. Sorted. I check the format before use, not lost anything.