How to fix Time Machine “Disk Not Ejected Properly”: “Backups of [mac]”
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.
On the Synology side, do configure WOL for the right port under Control Panel > Hardware & Power > General.
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?
As for the WOL packet side of the business, Time Machine does send the magic packet, and DSM has HDD hibernation enabled by default. I was able to find some information on older Macs not giving enough time for drives to literally wake up. Not putting any drives to sleep on NAS does sound a plausible fix, but an inefficient one at that. For home and small office uses, hibernation does go a long way.
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.
updated Sep 25, 2023: added Synology WOL part.