Solved - Slow Time Machine Encryption

I am encrypting my Time Machine backup. It has 3.2 TB of 4 TB available. So far it has been encrypting for over 24 Hrs and is only at ~25% done. Is this normally about how long it takes?

It seemed to take long for me too. Do you mean 3.2 TB is the size of your TM? Mine was around 500 GB and I think it took the whole night.

I should have made this clear. The TM backup is 800 GB. I have 3.2 TB Free on the 4 TB hard drive.

How is it connected? If usb 2 it will take a long time.

It’s a 2018 Mac Mini using a USB-3 port.

I just found this and am reformatting/reconfiguring TimeMachine following this advice. Will post my experience.


Entering this in

sudo sysctl debug.lowpri_throttle_enabled=0

is known to speed up Time Machine in general, and I assume (but do not know for sure) that it would speed up encryption as well.


Using the method as suggested in this article, I was able to create an encrypted Time Machine on a 4TB HD (backed up 800 GB of data) in about four hours.

Thank you for all of your replies/suggestions.

This is what I do too. It has the added benefit that data is never unencrypted on the backup drive, something that’s especially troublesome for SSDs, should you be fortunate enough to be using those for backups. (But at least the encryption is fast on an SSD)

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Apologies for resurrecting an old thread but I recently ran into the same issue of an excruciatingly slow initial backup and followed the advice on Chris Carey’s blog (linked to by @neonate) to encrypt the disk first. He also mentions selecting the Encrypt backups option under Time Machine preferences, which I did. However, I wasn’t prompted to set a password when doing so in contrast to the options presented when setting an unencrypted disk up previously. I wonder if this is so as the disk is already encrypted. Would I be right in assuming that the encryption password for the disk will work for Time Machine as well?

I am pretty sure this is a correct. I disconnected the Time Machine HD from my mini and connected it to my MacBook Air. I entered the Time Machine password and was able to access the files on the Time Machine HD.

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Many thanks for linking to this post! You made my day! :slight_smile: