Time Machine not deleting backups as NAS disk becomes full

Question

Level 1

59 points

Time Machine not deleting backups as NAS disk becomes full

2020 M1 MacBook Air, 16GB RAM, 1TB SSD, MacOS 14.7.1 (Sonoma)

I’m using a Synology NAS for Time Machine backups and hit an interesting problem today. The NAS is an 8TB Raid and used as a music server as well as TM. It is not partitioned and the music folder takes up less than 1 TB.

Today a backup failed for lack of space. Checking the NAS showed that TM had used up 7.75 TB of space. When I opened Time Machine, I saw that there were only two backups, all the older ones were in fact gone but I find it hard to believe that two backups of a 1TB internal SSD would take up almost 8TB. Using the NAS control panel interface I deleted the sparsebundle and successfully completed a backup from scratch in about 20 minutes.

Why did it not even try to delete old backups as it is supposed to do once there was not enough space?

For years I used a Time Capsule but after Apple stopped making them, I switched to a NAS. Just as I did when using the Time Capsule, I also use HDDs connected to our two laptops but they are not connected to the laptops 24/7. I do not use cloud backups at all.

MacBook Air 13″, macOS 14.7

Posted on Dec 4, 2024 10:11 AM

Reply

Answer 1

mudbucker Author

Level 1

59 points

Dec 5, 2024 1:07 PM in response to mudbucker

I have been poking around the internet for information about this and it appears this is NORMAL behavior. On a network drive, TM creates a sparsebundle file and then keeps adding to it over time. Of course, the sparsebundle gets larger over time as more changes get backed up.

Apparently TM has to complete the scheduled backup before it can start deleting older backups. If there is not enough space to increase the size of the sparsebundle, the backup fails. Why I never saw this with my old Time Capsule I do not know, but now I realize I have to keep track of the space on the network drive on a regular basis and when it approaches being full, I have to delete the sparsebundle and start a new one. I do not see any other option.

I wish Apple’s help pages would explain this behavior.

Reply