Total number of directories in an Azure subscription

Hi Vignesh, 

Here is the limits for Azure Active Directory

https://docs.microsoft.com/en-us/azure/azure-subscription-service-limits#active-directory-limits

There is no specified maximum number of directories on any official documentation I could find. However, looking at the document above a single user can belong to at least 500 so therefore you can have 500 directories at least in the azure account.

Regarding subscription, the following articles states that multiple subscriptions can trust the same Azure AD directory, but each subscription can only trust a single directory per article

https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/active-directory-how-subscriptions-associated-directory

It also states that all of your users have a single "home" directory for authentication. However, your users can also be guests in other directories. You can see both the home and guest directories for each user in Azure AD. 

You control the access to resources with RBAC on the azure subscription

https://docs.microsoft.com/en-us/azure/role-based-access-control/role-assignments-portal

Hope that helps

Best, Chris