Synology Time Machine Out of Space -- Why won't it delete old backups

I am using a DS620slim for Time Machine backups. My Mac runs 10.15.6 and it completed backups a day ago without issue.

I've created a shared folder with a specific user and a disk space quota to prevent time machine from consuming all my NAS space.

I've now reached the point where the shared folder is near at its quota limit, however, TM does not appear to be deleting old backups. Instead, attempting to backup gives me this error:

Why aren't old backups getting deleted automatically?

This is the process used to limit space is the shared folder quota:

Solution 1:

For me it worked after I disabled the Recycle bin on the Shared Folder. When Time Machine tried to delete old backups it moved them to the Recycle bin instead which causes the Shared Folder to never decrease in size.

Solution 2:

I would open a support ticket with synology. You have excellent details and perhaps they have a patch or better setup procedure for your specific version of macOS and storage software.

• specifically ask them if you could be using a sparse bundle for storage and if they can automate compacting of that bundle

As for your existing backup date - since space is tight, I would manually clean up some old backups using command line tools. Check for sparsebundle files which optimize network traffic and also need to be compacted periodically if space gets tight.

• How can I manually delete old backups to free space for Time Machine?

As you delete a few old backups, you can watch how much space is cleared and then attempt a backup after each cleanup.

Lastly, if you think you have enough space and don’t agree with the estimate for needed space, exclude some large folders and/or system files temporarily from backup and attempt a more limited backup. Eventually if you exclude enough “space” you can often get a small backup to run. After successful backups, the automatic pruning is more vigorous in my experience. After a few hours of clean runs, reverse the exclusions and see if your intended coverage now works with your storage.

Don’t overlook using an inexpensive direct attached disk as well to get one clean backup to a new destination that will let you know the Mac data is good and the problem is only with the synology side or existing data.

• https://support.apple.com/en-us/HT201250