Wednesday, March 16, 2016

Massively Speed Up Time Machine Backups

Keir Thomas:

Open a Terminal window, which you’ll find in the Utilities folder within the Applications list, and paste in the following, typing your login password when prompted:

sudo sysctl debug.lowpri_throttle_enabled=0

This command prevents Time Machine’s backup process assuming a low CPU priority, allowing backups to complete insanely quickly. In fact, you’ll see MB and GBs tick past on the Time Capsule progress display in a second-by-second fashion (provided your Mac isn’t very busy with some other task).

Alas, this command is forgotten when you reboot.

I suppose it’s a feature that Time Machine runs at a low priority by default, but this makes it much slower than other backup methods. Sometimes you’re waiting for it to finish and just want it to go faster. And with SSDs, running a backup doesn’t slow down the rest of the system as much, anyway.

Update (2016-03-16): Gwynne Raskind:

Make it stick with echo 'debug.lowpri_throttle_enabled=0' | sudo tee -a /etc/sysctl.conf (SIP-safe).

(however, I agree with the comments which suggest it’s questionable to do this on a global basis)

Update (2016-03-17): Rosyna Keller:

CPU isn’t throttled. The bottleneck is disk I/O. (lowpri_throttle_enabled is an I/O throttle, not a CPU throttle)

You can independently confirm it’s an I/O throttle by looking at the source that uses it.

There are even different throttles used depending on if the device is seen as an SSD or not an SSD by the system!

OS X detects drives in most USB/FireWire enclosures as non-SSD, even if they are SSDs

Update (2016-03-18): Daniel Jalkut:

As an experiment I disabled the low priority support as outlined in the post, and was curious to know whether it would affect the massive performance problems I suffer when browsing Time Machine history from my OS X Server hosted network backup volume.

It did seem to massively improve that experience.


If indeed I/O priority is throttled for Time Machine, please consider disabling that throttle or raising the priority while browsing backups. In this modal state it would seem like a reasonable thing to consume more of the computer’s I/O capacity in the name of providing a more responsive user experience.

Update (2017-10-13): St. Clair Software:

App Tamer 2.3.3 is now available – it’s a free update for App Tamer 2 users, and a $7.95 upgrade for version 1.x users.

It adds a checkbox that speeds up Time Machine backups, something that’s really helpful if you only plug in your backup drive occasionally, resulting in Time Machine needing to copy lots of data.

5 Comments RSS · Twitter

I haven’t checked this at all, but doesn’t this *debug* option tell the kernel to disable CPU throttling for each and every task that has a low priority? If so, wouldn’t it be a better idea to specifically give the Time Machine related processes a higher priority?

@Marco I think you are right. I’m not sure what else this affects. That’s why I would be more likely to use this command for a particular session than to use Thomas’s launchctl method.

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