Several months ago I bought a maxed-out MacBook Air to replace my old gen 1 MacBook Air. Everything ran faster on the new machine – well, nearly everything. To my disappointment, Time Machine backups were even slower than before. Very odd.

But with that clue, I guessed that the speed of Time Machine backups were being artificially inhibited. It didn’t take much web searching to confirm my surmise. And to discover how to defeat the speed inhibition. This Terminal command does that:

%> sudo sysctl debug.lowpri_throttle_enabled=0

(You'll be prompted to enter your admin account PW)

That reduced my typical backup time from about 3 hours to about 30 minutes. Yes!

So why does Apple inhibit the speed of Time Machine backups? Apparently most folks run backups in the background, and don’t want Time Machine to steal too many CPU cycles. But I do it differently, like this:

1. Disconnect from Internet.
2. Run a Malwarebytes scan.
3. If clean (it always has been) run a Time Machine backup.
4. Reconnect to the Internet and resume operations.

That way, I can be reasonably confident that all of my backups are clean. But my MacBook is off-line until the backup finishes, so I want it to finish ASAP, and the “sudo sysctl…” command helps a lot with that.

Two caveats:

#1 – Unless your /etc/sudoers file enables your user account, you’ll have to execute this command from your admin account. No big deal.

#2 – A reboot appears to restore the old-and-slow Time Machine backup mode, so I edited a function, which I named “fastback”, into my ~/.bashrc file to make it more convenient to set the fast mode:

function fastback () {
sudo sysctl debug.lowpri_throttle_enabled=0
}

No doubt folks that use sh or vi, rather than BASH, as their Terminal command interpreter will know of an equivalent method. Happy fast backups, all!

P. S. If for some reason you want to restore the old-and-slow Time Machine backup mode, this Terminal command will do that:

%> sudo sysctl debug.lowpri_throttle_enabled=1

Hey PS, this is great news for me because I have the same issue with long backups.
Can you give a little more details on how to do this?
If it isn't too much trouble, a step by step "How To" would be very helpful.
Thanks

3 hours? Wow.
Mine runs every hour when on mains power, takes minuets but I never timed one. I just let it run in the background. Done it that way for several years, currently on a 15" 2018 MacBook Pro with an over half full 1TB SSD, 2.9 GHz Intel Core i7, and 16GB Ram.

The file /etc/sysctl.conf exists to configure sysctl options across boots. It is a text file that can be edited with a text editor with a very simple syntax. Of course, you have to be root (superuser) to change it.

To append the above sysctl to the file so it will be active after boot every time do this in a Terminal window:

sudo echo "debug.lowpri_throttle_enabled=0" >> /etc/sysctl.conf

Be careful when editing this file, a prudent administrator will make a safety copy before making changes.

quote:

Originally posted by Cousin Vinnie:
Hey PS, this is great news for me because I have the same issue with long backups.
Can you give a little more details on how to do this?
If it isn't too much trouble, a step by step "How To" would be very helpful.
Thanks

Sorry, but with my limited ability to explain things, I don’t think that I can do much better than my OP.

If your Mac is portable, I suggest that you take it to an Apple store and show an employee my post. That employee will understand it and demonstrate the procedure.

If your Mac isn’t portable, print a copy of my OP and show that to an Apple store employee, who will explain better than I can.

quote:

Originally posted by cparktd:
3 hours? Wow.
Mine runs every hour when on mains power, takes minuets but I never timed one. I just let it run in the background. Done it that way for several years, currently on a 15" 2018 MacBook Pro with an over half full 1TB SSD, 2.9 GHz Intel Core i7, and 16GB Ram.

Well, yes, if you have Time Machine set to backup automatically every hour there won’t be many changed files to backup.

But as I noted in my OP, I run backups only after I’ve disconnected from the Internet, and get a clean Malwarebytes scan, so all of my backups are clean. I reconnect to the Internet only after the backup is complete. I have auto backup disabled, and backup only once a day, so there are many changed/new files to backup.