High CPU usage by diskimagesiod during Time Machine backups on 2021 5K iMac

In Disk Utility>View, select Show all Devices, highlight the top left entry.

Run Disk First Aid on all items in the left panel, from top down.

Are you running any VPN, Anti-Virus, or Cleaning apps?

Eject your TM drive for a test.

I have no idea why it worked, but it did work. After force-relaunching Finder, the process diskimagesiod went from >900% CPU usage to fluctuating around the 7% range. And the backup that was in progress kept going.

M1 Pro MacBook, on 15.1.1

Try disabling the Firewall.

Hey all, I'm on a Macbook Pro M1 Pro, and I've had this issue since Sequoia 15.0 (Currently on 15.1.1) most times when Time Machine has been backing up over wifi to my USB-connected NAS through my ASUS router.

Tonight while this was happening I opened Force Quit and chose to relaunch Finder (no reasoning behind this choice, I was just frustrated). Immediately the CPU usage dropped down to normal/expected levels.

I have no clue if this will help others, or if this is mere coincidence, but thought it was worth a post.

Same here, happens on 15.0, 15.1, and 15.2. I tried to renice the diskimagesiod process, no effect. I tried editing the plist to change the process type from "Interactive" (which it isn't and shouldn't be) to "Background" (a whole adventure of disabling SID, making filesystems writeable, etc.), but when I reboot, the plist reverts and the problem remains. The fix seems simple, just have that process either run at lower priority or limit its CPU usage, but MacOS won't let me do either of these things.

Just letting you know that this problem occured also to me - always during TM backup.

Seems than occasionally reopening Finder may temporarily solve problem.

Relaunched the finder. Now it looks just fine. Weird.

And the volume was list empty. Now repopulated.

M2 MacBook Air with 15.3

Hi there.

I have the same issue since upgrade to 15.0. Still persists in 15.0.1. I am on a 16" MBP M1 Pro, and its maxing out all 10 cores to 100%!!

It has to do with timemachine backup. If I stop the TM backup, "diskimagesiod" disappears.

Not sure if its relevant, but I am using a sparsebundle image in the TM backup HDD.

Any help would be appreciated!

Disabling the Firewall seems to help reduce the length of the CPU load to 100%

When in doubt... kill the Finder process! Well, lets see if its repeatable and not a coincidence. Maybe its the bread crumb we need to find root cause.

Well, looks like you got 27 'Me too's as of this writing. I'll add my data points fwiw. MacBook Air M2, Timemachine connected to a RaspberryPi NAS. CPU jumps to 900% thereabouts. Lasts about a minute for me when staring at Activity Monitor. Sequoia 15.1 . Perhaps next time i'll see if i can't drill down and get a thread count. Maybe its something crazy high? Anyway.... just another data point.

I have the same issue. My device is Mac mini 2018. The system usage becomes more and more worse after hibernation/wakeup several loops.

After a refreshing reboot, the system has ~5~8% usage with slient status, I use the Mac with KiCAD, FreeCAD, Safari, and Notion. Weeks ago, the system has ~20~50% usage in slient status even though I don't run any applications. The box is too hot and the fan becomes crazy.

This situation comes from 15.0 to 15.2, and no any improvement occurs. If the 15.3 still has this problem, I will fallback to 14.6.

BTW, I application list doesn't have Time machine, firewall and Anti-virus applications. When this problem occurs, I can't find out any conspicuous high-usage application in the active monitor so that I can't decide to terminate which app.

Saw the same behavior on an M2 macmini running Sequoia 15.2. The load came back soon after the relaunch, though. Only mentioning this because when I looked at System Settings Time Machine while the load was on, the volume list was empty, which was a bit disconcerting. As soon as I relaunched Finder, the list was back as expected.

Is this how you did it?

Time Machine > how to back up to a sparse… - Apple Community

Thanks.

I tried all of this as soon as the problem occurred. Without success. It is interesting that the error does not appear when using a usb hdd, but only when using a NAS. It doesn't matter if via Wifi or LAN. This was not a problem in previous versions of MacOS.

I do not use any antivirus or cleaning software.