A company has several petabytes of data that must be retained for 7 years to meet regulatory requirements. The compliance team asks the security officer to design a strategy that prevents any modification or deletion of the data. Which solution is the most cost-effective?

The most cost-effective solution for petabytes of data with a 7-year retention and immutability requirement is Amazon S3 Glacier with Vault Lock. S3 Glacier is significantly cheaper for archival storage than S3 Standard or S3 One Zone-IA. Vault Lock enforces immutability (WORM - Write Once Read Many) for the specified duration, preventing any modification or deletion, even by the root user, which satisfies the compliance team's request. S3 Object Lock in compliance mode also provides immutability but S3 storage tiers are more expensive than Glacier for long-term archives. Governance mode allows some users with special permissions to override or delete objects, which doesn't meet the strict immutability requirement. Transitioning data to Glacier via a lifecycle rule is an option, but directly uploading to Glacier with Vault Lock is simpler and often more cost-effective for data that is immediately archival.