Storage and Database Services
Object, block, and file storage
Alibaba Cloud offers OSS (object storage), cloud disks / ESSD (block storage for ECS), and NAS (shared file storage). Choose by access pattern: OSS for unstructured objects via HTTP API with high durability and lifecycle policies; disks for low-latency single-instance block I/O; NAS for shared POSIX access across multiple instances. Traps: using a disk where multiple instances need concurrent shared access (use NAS), or storing frequently rewritten small files in OSS without considering request costs.
OSS specifics
Buckets have storage classes (standard, infrequent access, archive) and lifecycle rules to transition or expire objects. Versioning protects against overwrites and deletions. Bucket policies and ACLs control access. Know that OSS is eventually consistent for overwrites in some contexts and that cross-region replication is configured explicitly.
Databases
ApsaraDB RDS is managed relational (MySQL, PostgreSQL, SQL Server). PolarDB is a cloud-native relational engine with storage-compute separation and high performance. Redis for caching, MongoDB for document data, AnalyticDB for analytics. Managed services handle backup, patching, and HA via primary/standby replicas. Read replicas offload read traffic; they do not automatically provide write scaling.
Worked rule of thumb
Shared configuration files across many ECS instances → NAS. Backup and archive of media → OSS with lifecycle to archive class. Transactional app → RDS with standby and read replicas. Hot cache → Redis.
Exam framing
Match the access pattern (shared, object, block), consistency, and durability needs to the storage type before considering cost.