How to get 1 chain with rotating differentials

ilnot, welcome to these user forums.

There isn't a way to do exactly what you are asking with just keeping a specific number of differentials without creating a new full backup, which is how the automatic cleanup rules work.  Part of the reason for this is that after a time, the size of the differentials can approach or equal the size of the full backup file due to the number of changes which are being captured.

What you may need to consider here is if you can split your backup source data up, i.e. I would assume that the 2TB of data comprises of several different partitions, so creating separate backup tasks for the different partitions can help to reduce the size of backup data plus make it faster to perform.  

Note: It is recommended to do a Disks & Partitions backup rather than 'Entire PC' backups as these can include any other drives connected to the system, including your backup drive.  If you have multiple disk drives in the system, then keep these backed up in separate tasks, one per disk.

P.S. I would recommend posting directly in the Acronis True Image 2017 Forum for future questions as this Best Practices forum is not as active and new topics can be missed.

Thanks for your quick response.

I understand what you're saying about the differentials growing in size, that is why I  got an 8TB backup drive. So even if the 7 differentials grow to an average size of 750GB I'll still have enough room. This way I'd only have to create a new full backup once every 3-6 months. Also, I am only selecting the drives that I want to be backuped up.

I've been a fan Acronis for a while, it is a shame this is impossible.

You can take the option to 'Create only differential versions after the initial full version' which will create you full backup and the chain of differentials, but you then have to manage the differentials manually and also decide when you need to start over again with a new full backup.  This option doesn't give you access to the automatic cleanup options that would manage the size of backups for you.

If you go with option, then configure the Notifications tab to 'Show notification message on insufficient free disk space' and set a value for 'Notify me when free disk space is less than:'  and set this for GBs rather than the default MB's

Thanks, that is a workable soloution but of course more work for me.

What about these settings in the attachment. How does Acronis manage the size of the backup? Deleting the oldest differential? Deleting the oldest backup file, which would be the full? Except in this case I have "Do not delete the first version" checked, so how would it handle the size management in this case?

Ticking the option to not delete the first version means that the file with the name including _full_b1_s1_s1.tib will be kept, but that later full backup versions would be deleted according to the other rules set.

Please remember that differentials can only be applied to the initial full backup for the backup chain they belong to, so you cannot associate a file such as _diff_b5_s2_v1 with any full backup other than _full_b5_s1_v1 which doesn't make keeping the first version full backup file very useful unless this was created immediately after a new clean install of Windows that you may want to go back to at some point.

Acronis automatic cleanup works only on completed backup version chains, so per your capture image, this would be 1 x Full backup plus 90 Differential backup files.  The oldest backup version chain is only deleted after the next version chain has been started successfully with a new full backup file.

If I understand correctly, when you set the option to keep the Backup size to 6TB, this is the size of completed version chains again, you would still need sufficient free space to create the next full backup file for the following version chain before cleanup frees up space by deleting the oldest backup chain.

I see. Thanks for all your help.