macOS, diskarbitrationd

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?

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? :-}

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.

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.

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.