I had an APFS (Encrypted) disk which I chose for Time Machine backups on macOS Catalina.

I was asked if it was OK to erase the disk (Time Machine on macOS Catalina dosen't support APFS).

I answered yes and disk was formatted as "Mac OS Extended (Journaled, Encrypted)".

Initial backup is done, but encryption is taking forever.

Running diskutil cs list reveals Converting (forward) and Conversion Progress: 2%.

What does Converting (forward) mean and was my data backed up in clear (meaning it was encrypted during initial backup)?

Why is it taking forever to encrypt data given disk was formatted as "Mac OS Extended (Journaled, Encrypted)" before data was backed up?


  • 1
    I learned a long time ago that is faster, and IMO better, to format it Mac OS Extended (Journaled, Encrypted) with the disk empty and not being used for anything until it's encrypted and then start using the disk for whatever. I also always start the encryption at night when I'm done with the computer and let it do its thing while I sleep. Need to temporarily set the system not to sleep too! Apr 2, 2021 at 14:22

1 Answer 1


Converting "forward" means that direction is from not encrypted -> encrypted. I.e. you started with a blank disk and enabled encryption.

It is possible to do a conversion in the opposite direction if you later decide you do no want your disk to be encrypted.

Your backup was encrypted - it is not stored in the clear when encryption is enabled.

Encryption does take a long time, yes. It is intentionally throttled to not consume system resources, but takes place in the background. You can keep using the computer and the disk while it is working.

It can be a pain if you're encrypting an external disk and need to keep it connected for a long period of time, but unfortunately that is normal.

  • 1
    Thanks for helping out... would you happen to know why formatting and encrypting the disk first to "Mac OS Extended (Journaled, Encrypted)" using "Disk Utility" and then enabling Time Machine makes the process significantly faster (hours vs days)? My understanding is that both options result in having encrypted backups.
    – sunknudsen
    Apr 2, 2021 at 15:18
  • Also, you mentioned "Encryption does take a long time, yes.". Why does it take significantly longer than initial backup if initial backup is encrypted? Is TM encrypting the whole disk rather than just the backup? If so, why whole disk when selecting "Encrypt" in Time Machine preferences vs when formatting and encrypting the disk first to "Mac OS Extended (Journaled, Encrypted)" using "Disk Utility"?
    – sunknudsen
    Apr 2, 2021 at 15:21
  • Yes, TM does encrypt the whole disk, and not just the backup. This is it can take longer to encrypt than just doing the initial backup.
    – jksoegaard
    Apr 3, 2021 at 12:40
  • You haven't detailed exactly what you did and what happened before that. But consider a case where you have a completely factory new, blank disk that isn't partioned yet - and you choose to partition and format it as Mac OS Extended Encrypted using Disk Utility. In this case, you can live with the system just formatting the drive and setting the encryption up. Essentially encrypting very little. However, if you have an existing USB drive that you have used for file storage, and then give it to Time Machine and say "please use this for encrypted backups" - then TM would have to ask for...
    – jksoegaard
    Apr 3, 2021 at 12:42
  • ... everything on the disk to be encrypted. I.e. you could have other data on there from previous (i.e. even if you delete files from the disk, their data is not actually removed from the disk - it is still there if someone goes looking "behind the scenes"). In this case you want the whole to be encrypted, and the whole disk overwritten with an encrypted version of what was there before.
    – jksoegaard
    Apr 3, 2021 at 12:43

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