Azure Storage account tiers — Hot, Cool, Archive — pricing and access patterns

Azure Blob Storage has four access tiers. Choose by read frequency and retrieval latency tolerance.

Tier	Storage cost	Read cost	Min storage duration	Retrieval latency
Hot	highest	lowest	none	ms
Cool	lower	higher	30 days (early-delete fee)	ms
Cold (preview/GA)	lower than Cool	higher than Cool	90 days	ms
Archive	lowest (~$0.002/GB)	highest	180 days	hours (rehydration)

Decision flow

1. Read several times a day? Hot.
2. Read maybe once a month? Cool.
3. Read once a quarter, can wait 1 hour? Cold.
4. Compliance retention, may never read? Archive.

Lifecycle management — automate the move

{
  "rules": [{
    "name": "auto-tier",
    "type": "Lifecycle",
    "definition": {
      "actions": {
        "baseBlob": {
          "tierToCool":   { "daysAfterModificationGreaterThan": 30 },
          "tierToArchive":{ "daysAfterModificationGreaterThan": 180 },
          "delete":       { "daysAfterModificationGreaterThan": 2555 }
        }
      },
      "filters": { "blobTypes": ["blockBlob"], "prefixMatch": ["logs/"] }
    }
  }]
}

Apply via the portal, ARM template, or az storage account management-policy create.

Rehydration from Archive

Set the desired target tier; Azure begins copying. Standard priority — up to 15 hours. High priority — under 1 hour for blobs under 10 GB, at higher cost.

az storage blob set-tier --tier Hot --rehydrate-priority High \
  --account-name myacct --container-name logs --name 2024/q1.tar

Hidden costs

• Early-delete fee — moving a blob out of Cool/Cold/Archive before the minimum duration charges the remaining days as if it had been kept.
• Read against Archive without rehydration fails. Application must check accessTier and handle "Archive" specifically.
• Operation costs dominate small-blob workloads. 1 million writes to Hot is cheap on storage but the per-operation fee adds up.

Common patterns

• Server logs. Hot 7 days, Cool 30 days, Archive 365 days, delete after 7 years.
• User-generated content. Hot for new uploads, demote to Cool after 90 days of no access (daysAfterLastAccessTimeGreaterThan requires Last Access Tracking enabled).
• Backup snapshots. Direct to Archive on creation if rehydration latency is acceptable.

Geo-redundancy is a separate axis

LRS, ZRS, GRS, RA-GRS — these affect durability and disaster-recovery topology. Pick tier for cost, redundancy for RTO/RPO independently.