the max_over_subscription_ratio is supported by the Manila Driver, but its functionality is implemented as follows:
1. Settting the max_over_subscription_ratio to a value above than 1 (1.5 for example), then it is possible to create multiple manila shares, whose total summation exceeds 1.5 times the total capacity of the available aggregates.
In your case, for a 53TB aggregate and a max_over_subscription_ratio value of 1.5, then there can be multiple shares created, whose total capacity will be permitted to be <79T.
The size of a single share will not exceed 53T.
Also, you can probably get a quicker response by posting on the #openstack channel in our Slack workspace. You can join at netapp.io/slack