The three shapes
Object storage (S3, Blob, GCS) holds immutable blobs behind an HTTP API and scales without limit — ideal for media, backups and data lakes. Block storage (EBS, Persistent Disk) attaches to one instance as a raw volume for databases. File storage (EFS, Filestore) provides shared POSIX semantics over NFS.
Durability and consistency
Providers quote eleven nines of durability by replicating across facilities; that is durability, not availability, and it is not a backup — a delete or an encrypting attacker replicates too. Enable versioning, object lock and cross-region replication for anything you cannot lose.
Classes and lifecycle
Hot, infrequent-access and archive tiers trade retrieval latency and per-request cost against storage price. Lifecycle rules move objects automatically by age. Egress — data leaving the provider — is usually the surprise line on the bill.