info request

Hello and greetings to all the community.

We are evaluating the product Zextras and we came up with some questions to bring to your attention.
If we were to apply the "Retain Data Backup" equal to 0 days, so always entirely consistent, theoretically we could be with the backup volume larger than that of exercise.
But while on Zimbra store is the ability to change the volume with the increase in employment of disk space, how can we emulate this feature with Backup Zextras to have the same characteristics?
We have to manage the exponential growth of the backup thus increasing storage?
We can not split the backup into the main volume and the secondary volume as well as Zimbra is for the store?