macOS, diskarbitrationd

TidBITS Talk
1

The root user process diskarbitrationd, as I sit here typing with no external volume mounted, mounting, or dismounting on the desktop, is taking 25% to 60% of the CPU cycles of my MBA (M1, 2020) running macOS 11.6.8, and it will routinely do so for minutes if not hours at a time. If I do connect an external drive, diskarbitrationd will take 99% of the CPU cycles for 5 to 40 seconds before anything appears on the desktop. (When it gets to the upper end of that range, I restart, and that seems to reset something so that my wait is in the lower end of that range, for a few days.) As far as I can recall, this started around macOS 11.4 or 11.5.

With those scanty details, can anyone suggest what is going on or what I should do to keep the problem from getting worse after a restart?

Has anyone seen this and then seen it get better with Monterey?

2

Not seeing anything like that diskarbitrationd cpu usage here. Unmounting maybe 1.5%, mounting 3% for a few seconds each. Option-clicking on a folder triangle w/ >6K items 7% for a few seconds. This on a Studio Ultra w/ Monterey 12.6, two external Thunderbolt enclosures w/ external SSD’s.

Time Machine bumps it to 0.5% briefly. I do not have Spotlight indexing the external volumes, but turning it on barely got a blip out of diskarbitrationd. Got me what it could be. Not normal? :-}

3

Thanks for that negative report. I recently restarted and diskarbitrationd is sometimes dipping into single digits for one refresh cycle in Activity Monitor, but it is typically 20% to 60%. In other words, a slight decrease on the lower end, but still pretty much nonstop activity. Again, that’s with no external volumes mounting, dismounting, or on the desktop.

4

Have you tried to boot Recovery and run First Aid on your boot drive?

Also I’ve seen diskarbitrationd go wonky on a failing external USB drive.

5

Thanks for that suggestion. It might be some time before I get to it, but I plan to try Recovery and First Aid.

All my drives in regular use are fairly new (I’ll guess less than three years old) and do not get a lot of use. The flip side of that is that they get mounted and unmounted, since I don’t leave them connected when I’m not accessing them. And some of them do have up to eight volumes. But it does not seem like any of that should cause a problem.

I restarted two days ago, and right now, diskarbitrationd is bouncing between 15% and 45% CPU usage (with an infrequent dip to single digits for one refresh cycle in Activity Monitor), with no external disks connected.