In Solana, you can use the account-based storage model with PDAs (Program Derived Addresses) to create a global hashmap. Each key-value pair can be stored in a unique account, with the key serving as part of the PDA seed. To calculate rent exemption, use Solana's get_minimum_balance_for_rent_exemption function based on the serialized data size. For a single global hashmap, manage entries via program logic, serializing/deserializing the keys and values efficiently with libraries like borsh.