Blob Storage Tiering: Hot, Cool, Cold, Archive — and the Lifecycle Policy That Pays for Itself

Azure Blob Storage has four access tiers. They differ on read price, storage price, and minimum retention. Picking the right one (and moving between them automatically) is the highest-ROI FinOps move on most subscriptions.

The four tiers

Tier	Storage	Read	Min retention	When
Hot	Highest	Lowest	None	Active data, last 30 days
Cool	~50% lower	Higher	30 days	Backups, monthly reports
Cold	~75% lower	Higher	90 days	Long-term archive, occasional read
Archive	~95% lower	Rehydration required (hours)	180 days	Compliance retention

The classic mistake

Teams set their account default to Hot and never tier anything. Years later, 80% of objects haven't been touched in 6 months and they're paying Hot prices for all of it.

The lifecycle policy that pays for itself

{
  "rules": [{
    "name": "tier-and-archive",
    "enabled": true,
    "type": "Lifecycle",
    "definition": {
      "filters": { "blobTypes": ["blockBlob"] },
      "actions": {
        "baseBlob": {
          "tierToCool":    { "daysAfterModificationGreaterThan": 30 },
          "tierToCold":    { "daysAfterModificationGreaterThan": 90 },
          "tierToArchive": { "daysAfterLastAccessTimeGreaterThan": 365 },
          "delete":        { "daysAfterModificationGreaterThan": 2555 }
        },
        "snapshot": {
          "delete": { "daysAfterCreationGreaterThan": 30 }
        }
      }
    }
  }]
}

Watch-outs

• Early-deletion penalty. Move out of Cool before 30 days and you pay the rest.
• Rehydration is slow. Archive → Hot takes hours. Don't archive things you might suddenly need.
• Last-access tracking needs to be enabled on the account before daysAfterLastAccessTime works.
• Append blobs can't be archived. Keep your log streams in Hot or Cool.

Run the policy. Wait a billing cycle. Compare the storage line. Your CFO will ask what changed.