Local NVMe for processing
Fast local disks support capture and post-processing. Retaining every published recording forever on the same filesystem eventually couples server replacement to a large data migration.
Retention changes the calculation
Monthly recorded hours, the media profile and the number of months retained matter more than registered users. Use the recording calculator to create a planning estimate, then measure real output from your deployment.
Storage is not a backup
Mirroring and external capacity improve resilience but do not replace an independent, tested backup. Decide separately how published recordings, raw archives and application metadata are protected.
The operational reality
BigBlueButton capacity depends on how people use media. Hardware specifications help narrow the choice, but your own load test, monitoring and failure plan turn that choice into a production design.