Hi @Michael Brough,
Q1: Yes, OneDrive for business doesn't need to draw from any sort of maximum pool the way that SharePoint does. OneDrive for work and school accounts is online storage space in the cloud that's provided for individual licensed users in an organization.
For most subscription plans, the default storage space for each user's OneDrive is 1 TB.
For information on OneDrive storage per user, you can check OneDrive in the Modern Work Plan Comparison or the Microsoft 365 User Subscription Suites for Small and Medium-sized Businesses.
Q2: If you want to upgrade from 1TB to 2TB, then you need to purchase OneDrive for Business (Plan 2). It costs $10.00 user/month and provides unlimited individual cloud storage. You can view this article:
Compare pricing and plans and the screenshot.
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