Blob access tiers
What it is
Blob access tiers optimize Block Blob cost by expected access frequency. Hot is for frequent use; cool and cold are online tiers for less frequent use; archive is offline long-term storage. The tier trades storage cost against access cost, availability, and—in archive—retrieval delay.
Why it exists
Most data (‘unstructured/marketing/backup/compliance’) is accessed rarely once written. Paying full hot-tier price for it wastes money. Tiers align cost with access patterns.
The tiers
- Hot: online tier for frequent reads or writes; highest storage cost and lowest access cost. It is the default for a new general-purpose v2 account.
- Cool: online tier for infrequent access; 30-day minimum storage duration.
- Cold: online tier for rare but still fast retrieval; 90-day minimum storage duration.
- Archive: offline tier for very rarely accessed data; 180-day minimum. Rehydrate to hot, cool, or cold before reading or downloading. Rehydration can take up to 15 hours.
- Smart tier: automatically moves eligible data among hot, cool, and cold tiers based on usage patterns. It does not include archive.
Tier can be set at the storage-account default for new blobs (hot, cool, or cold) or explicitly per blob. A lifecycle policy can automate rules-based tier changes; archive rehydration cannot be performed by lifecycle policy.
Northwind example
Northwind keeps current product images in hot storage, completed monthly exports in cold storage, and legal archives in archive. If a legal request arrives, the archive copy is not ready immediately; Priya starts rehydration and plans for the delay. The team does not move a file into cold for a week and delete it—early deletion charges still apply before the 90-day period.
How it fits (diagram)
Exam notes
- Archive is offline; it requires rehydration before content can be read or changed.
- Cool, cold, and archive can incur early-deletion charges when deleted, overwritten, or moved before their minimum duration.
- Access tier is a cost-and-availability choice, not a backup, retention, or authorization policy.
Related
blob-storage · storage-account · storage-performance · immutable-storage