mioan wrote:
• Thank you for your answers so far.
Some extra info:
The Macbook internal drive is 500GB.
The error is the same for two different backup destinations.
USB disk 1TB. Free space 100GB.
• Synology NAS folder share 1.7GB. Free space 100GB. I will increase the quota to 2GB to give enough space for a full backup to see if this error is because of the destination drive.
If the error message is accurate, it indicates that the problem is not on the destination. It says that if older backups were removed there is still not enough space. So the file system element that is behind the "null" is bigger than 1TB, which cannot be for a macbook hard disk of 500GB.
Make sure the Synology is not running the effected Samba 4.22.
Though I doubt the Samba incompatibility with Time Machine is the issue here, and doubt the capacity is an issue, twice the source capacity is very much a marginal choice at best. Per the late Pondini:
A general "rule of thumb" is, to keep a reasonable "depth" of backups, Time Machine needs 2 to 4 times as much space as the data it's backing-up (not necessarily the entire size of your internal HD). Be sure to add the size of the data on any other drives/partitions you want to back up.
But this varies greatly, depending on how you use your Mac. If you frequently add/update lots of large files, then even 5 times may not be enough. If you're a light user, you might be able to get 1.5 times to work, but that's subject to problems any time a large backup is needed.
And, of course, the larger the drive, the more old backups Time Machine can keep for you. A drive that's too small may only have room for a few weeks (or even days) of backups.
Unfortunately, it's rather hard to predict, and most of us have a tendency to add more and more data to our systems over time, so if in doubt, get a bigger one than you think you need now.
For local usage and the sizes of files involved in the local file churn, triple works well as a minimum. If you're churning VM guests for instance, you may or will need more.
But…
Given the reports of corruptions and attempted repairs on the input device, I’d back up your data a couple of times, erase, and migrate. Here, I’d probably boot Recovery and use Disk Utility to create a full copy of your data, or maybe use Carbon Copy Cloner to create a backup. Or better, two copies on the off chance one copy fails, or gets overwritten, or whatever.
Then erase and reinstall macOS, and migrate your files from your backup during the first-boot setup.
This path is the “I have a new Mac, I need to migrate my contents.” sequence.
This given the source corruptions, the potential for a hardware problem, and given you are having issues with the existing attempts to use Time Machine.
GPTs are not technical — far from it — and are not reliable reference sources. They can be useful for generating management mail memos, faux pas, bunk, and nonsense. There’s a much more descriptive word too, but for decorum.
