Encrypting HFS+ external HD triggers APFS conversion, even for Time Machine drives

Originator:mike.solin
Number:rdar://36385103 Date Originated:09-Jan-2018 05:00 PM
Status:Open Resolved:
Product:macOS + SDK Product Version:10.13.2
Classification:Crash/Hang/Data Loss Reproducible:Always
 
Summary:
On macOS 10.13.2, right-clicking on an external HD formatted as HFS+ triggers an AFPS conversion.  Once complete, the encryption will proceed.  This is is a lengthly process, and is not desirable in certain situations (such as for a Time Machine backup drive).

Steps to Reproduce:
1.  Format an external HD as HFS+.
2.  Enable Time Machine on the external HD (optional).
3.  Right-click on the external HD in the Finder, and click “Encrypt <drive name>…”

Expected Results:
4.  The drive will be encrypted.

Actual Results:
4.  The drive is converted from HFS+ to APFS.
5.  The drive is encrypted.
6.  Upon finally remounting (my 2 TB USB 3.0 drive took several days for this process to occur), you will receive a notification that a backup cannot occur, as Time Machine requires HFS+.

Version:
10.13.2

Notes:
Once following these steps, your only option is to format the Time Machine drive, losing data in the process.

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