Q: No more space, Time Machine backing up several Minis to Time Capsule

I don´t know if is got to do that the backups in T.C. are just a single disk image (Sparse Disk Image Bundle) for every account, not folders with dates, like my macbook does when using T.M. to an external disk.

No. That's actually the way Time Machine is designed to work. The method is different between network drives and those locally attached.

Please check out the following Pondini article to see if it can help.

Time Machine needs a fair amount of free space on a disk to work. And when you are using 5 different computers then you can expect there will be times that 2 or 3 are doing backups together and will flood the free space.

TM has been less than great of late in terms of handling updates and corruptions.

What model is your TC? What size hard disk?

Do the mini's use wireless? If so there is no slow down in using USB drive plugged into the TC and locate 2 or 3 of the backups there.

On a Gen3 TC with 1TB disk I would recommend an internal disk upgrade or total replacement.

the Mini's they do connect via WiFi (300 Mbps. to router, router 1 GB to the TC).

This can be an issue.

Apple DNS has issues with the TC location if the mini is not connected directly to it, either by wireless or ethernet. Not everyone has issues but some people do.

The TC is a 2011 model A1409, 4th generation, 3 TB

The Gen4 has a hardware problem as it ages.. it is now >3 years old .. maybe up to 5 years. It might be time to seriously look at another method of handling backups.

How much free space do you have on the TC disk??

Free space is calculated on a bunch of factors.. 10GB is just not enough on a 3TB drive. It is not the size of the backup.. it is how much of the backup needs to be used to add the files to it.. and the backup for each of the mini's will be 10x or 100x 10GB.

Yes, I know, and Im considering it, you know if the new version handles better this scenario?

New one is faster wireless.. otherwise it is no different. It will not handle the situation better and I fear it could be worse.

However I would be seriously thinking and planning to replace the Gen4 TC. Sometimes they can die very suddenly.

As a stopgap, I would buy a 4TB (that is about the sweet spot) USB external hard drive and plug it into the TC.

I would then move the 3 largest sparsebundles to the USB drive and reconfigure the mini's that correspond to backup to the USB. (There are other methods of course.. you can archive the TC to the USB drive.. then simply erase the TC and start a whole new set of backups. Or redirect the Mac to keep using the backup on the USB drive instead)

OR you can plug a self powered USB 2.5" drive into the minis and make a bootable clone using Carbon Copy Cloner.. and stick with that for your backup or partition the disk and use it for TM as well. Local backups with TM are far more reliable than to network target.