New iMac with Monterey - External Drives Disconnect When Display Sleeps

I discovered that if I select "Sleep" from the Apple menu for our new M1 2021 iMac, our hourly Time Machine backups work fine even while the iMac is asleep. So I set "Turn display off after" to "Never", set my Screen Saver to the "Message" screen saver with spaces for a message, and set "Show screen saver after" to 10 minutes. So I now have a low impact screen saver if I'm going to be away for a little while and the "Sleep" function if I'm going to be away for a longer spell.

This is different from our older iMacs, where we can separately specify when the display turns off versus when the hard disks turn off (so we can automatically turn off the display after 10 minutes and the hard disks after 3 hours) and never have Time Machine backup problems even on older Iomege Firewire disk drives. On the older iMacs, we routinely turn the display off with Control+Shift+Eject when we are stepping away for a little while.

I can't find any clear documentation on exactly what is supposed to happen with Monterey 12.3 on an M1 2021 iMac when the "Sleep" function is invoked, versus what happens when the display is turned off automatically after a specified time period. (After talking with Apple Support, I still don't have a clear idea.) But given my experience, there is something odd going on with either the M1 2021 iMac on Monterey 12.3 or our older Firewire 800 Iomega disk drives that causes Time Machine hourly backups to fail on backing up certain selected files if the display has gone to sleep after a specified time period.

Hcsitas

Perhaps things are simply flakey with Sleep on Monterey 12.3 running on an M1 2021 iMac. On another post (https://discussions.apple.com/thread/253541931?login=true&page=1), a long-time forum participant suggested not using either auto or manual sleep for now.

I thought my Time Machine failures were limited to when the displays were put asleep by the Energy Saver "Turn display off" option and were working when "Sleep" was invoked from the Apple menu. But then they started to fail on Sunday (always with being unable to backup a particular file, usually the "com.apple.LaunchSewrevices-3027-v2.csstore" file). I found a post saying (improbably) that Time Machine failures could be caused by having the Mission Control "Displays have separate Spaces" option unselected. (I have an external LG monitor connected to the iMac.) Since I had disabled "Displays have separate Spaces" on Sunday before Time Machine backups started to fail after invoking "Sleep" from the Apple menu, I reenabled it on Monday. Now Time Machine backups often--but not always--fail when "Sleep" is invoked from the Apple menu.

Also, on Saturday and Sunday nights, after invoking "Sleep" from the logon screen, my iMac "was restarted because of a problem" while asleep during the night, and the Problem Report started with "Attempting to forcibly halt cpu 0". I found a couple of posts saying Mac restarts while asleep could be caused by having the Energy Saver "Wait for network access" option unselected. Since I had unselected this option on Saturday at your suggestion, I tried reenabling the "Wake for network access" option on Monday, and the restart error did NOT occur Monday night.

hcsitas:

Thanks for your reply. I was able to reach Apple senior support and provide screen captures of the error messages and my Energy Saver settings. I asked them about a reformat and they said that an "Erase" with the Mac Disk Utility would have formatted the drive and I shouldn't have to redo it, since I did this before my first Time Machine backup with the new iMac. (That comports with the documentation I've found online.) I don't have another unused external drive I can reformat to test with.

Apple Support asked me to make a video of our iMac when the display wakes up with the error message from a scheduled hourly Time Machine backup that occurred while the display was asleep, open the detailed error message with the video running, and send that video to Apple Support, then contact Apple Support and work with them to provide them with system logs. I'll do this when I have some time.

Power Nap is an option available for some Macs under System Preferences | Battery for laptops and under System Preferences | Energy Saver for desktop computers, but is NOT available on our two older iMacs because they don't have an SSD drive. It is also NOT available for our M1 2021 iMac even though it does have an SSD flash drive, due to the "always on" technology of the M1 silicon chip. So on our M1 2021 iMac, Power Nap is on by default and can't be turned off (https://www.xda-developers.com/first-10-things-to-do-m1-mac/#3.3).

As I noted in my earlier reply above, I am okay with the results I've been able to achieve using the "Sleep" function on the Apple menu (where Time Machine backups are performed without error).

As a side note, Time Machine backups are NOT performed when no user is logged on and "Sleep" is select on the logon screen, both with our new M1 2021 iMac and our two old iMacs. I am also okay with that.

hcsitas:

I erased but did not format the Iomega drive I'm using for the Time Machine backup when we got our new iMac a few days ago. The initial full Time Machine backup on the new iMac ran fine. The hourly Time Machine backups work fine except when the display is asleep. I've captured the could not backup "knowledgeC.db" error once, and the could not back up "csstore" error three times now.

To be clear, the Time Machine backup fails ONLY when the display is asleep, and the failure is due to not being able to back up either the "knowledgeC.db" file or the "csstore" file.

Yes, I suppose it could be a problem with my Iomega Firewire drive and/or the adapters connecting it, but this happens ONLY when the display is asleep and NEVER when the display is active, so it certainly SEEMS like something on the iMac is triggering this backup failure.

Yes, I know hourly Time Machine backups work when the iMac is asleep due to selection of Sleep on the Apple menu. If I open the Time Machine disk, I can see the hourly backups that occurred while the iMac was asleep.

The issues with the three different "Sleep" functions (display "Sleep", Apple menu "Sleep", and logon screen "Sleep") in Monterey 12.3 on our week-old M1 2021 iMac (with an Iomega 1 TB Firewire 800 drive for our Time Machine drive and an external LG Ultrafine second monitor) have turned out to be so convoluted that I've logged it as a separate post: Problems with "Sleep" function in Montere… - Apple Community