How to fix Time Machine “Disk Not Ejected Properly”: “Backups of [mac]”

by Rian

Being a Mac user myself, one of the biggest features I recommend is Time Machine. Personally a well-designed backup system alone can make up enough reason to choose an OS for home use. I highly recommend using a Time Machine backup via NAS, for the benefit of traveling light and separating out a backup drives physically.

Symptoms

macOS delivers Time Machine with a bizarre quirk as of late; it frequently displays a warning “Disk Not Ejected Properly” for NAS. I am experiencing this issue on both laptop (MacBook Air) and desktop (Mac Pro) coupled with Synology NAS. The real oddity is that the logs from NAS does not seem to indicate any kind of network failure. As such, other volumes mounted from the same NAS unit do not suffer random ejections.

The frequent “ejection” either halts or stops Time Machine backup from happening. This could be especially bothersome during the first backup, when it needs to create a backup of an entire drive.

Solution

Though it is not clear-cut why this works, disabling “Put hard disks to sleep when possible” fixes the problem. On desktops, the option is located under System Settings > Energy Saver. On laptops, it’s under System Settings > Battery > Options. Either toggle it off completely, or change the settings to never.

Afterthoughts

The said setting is a remainder of hard discs days in laptops and desktops. It was a common practice to turn this setting off when a similar error from an external drive would pop up after a sleep. Nowadays, HDD hacks and tips have become a minor subject. Most PCs available on the market are shipped with SSD as the primary, and HDD is usually considered a cheaper alternative. macOS has gone through similar transitions: from HFS to APFS, and from Fusion Drive to good ol’ regular SSD.

The problem is that I could not find enough documentations on how far that one on/off switch can or should govern in terms of drives. Internal drives have been upgraded to SSDs, therefore no spinning discs to power down. External drives could be HDD, but I recall the same option was notorious for causing issues with USB hard drives as not all of the drives were intended to be “put to sleep”. The most irritating would be any volumes or discs connected via network. Just, why? Why is this option attempting to control a network drive to begin with? Why is this option overriding actively working Time Machine?

Though I was able to fix my problem, and leaving the solution published as-is, I, for one, was more baffled than before. I’ll update the post if I find any relevant information on it.