Blob Storage and Access Tiers
😟 THE PROBLEM
Years of rarely viewed videos cost as much to store as today’s files.
😊 THE SOLUTION
Use blob access tiers and lifecycle rules to move old data to cheaper tiers.
- Paying hot prices for old data✓ Cool, Cold or Archive tiers
- Moving files by hand✓ Lifecycle management rules
- Need old data occasionally✓ Rehydrate from Archive when needed
Quick answer
Azure Blob Storage is object storage for massive amounts of unstructured data, such as images, videos, documents, logs and backups. Access tiers let you balance storage cost against access cost: Hot for frequently used data, Cool (stored at least 30 days), Cold (at least 90 days) and Archive (at least 180 days, offline, must be rehydrated before reading).
Exam objective: 2.3.1 Compare Azure Storage services. 2.3.2 Describe storage tiers. (Skills measured as of July 20, 2026)
Start with a question
Should last week’s photos and ten-year-old tax records cost the same to store?
No. You look at recent photos every day; old records almost never. Access tiers let you pay less for data you rarely touch.
Explain it like I’m 10
The technical explanation
| Tier | Best for | Minimum duration | Availability |
|---|---|---|---|
| Hot | Frequently accessed data | None | Online |
| Cool | Infrequently accessed | 30 days | Online |
| Cold | Rarely accessed | 90 days | Online |
| Archive | Long-term retention | 180 days | Offline (rehydrate first) |
Hot, Cool and Cold can be set as the account default; Archive is set per blob. Lifecycle management rules move blobs automatically.
Real-world business scenario
A video surveillance company
- The problem
- Recordings must be kept for 2 years but are almost never viewed after the first week; storage bills were huge.
- What they used
- Blob Storage with lifecycle rules: Hot for 7 days, Cool until day 90, then Archive.
- Why that choice
- Each video lives in the cheapest tier that still meets access needs.
- The result
- Storage costs dropped substantially while meeting retention rules.
When to use it and when not to
✓ Use it when…
- Images, videos, documents, backups, logs and data lakes.
✕ Think twice when…
- Archive for anything needed within minutes.
- Blobs as a shared drive for Windows users (use Azure Files).
Interview preparation
Say your answer out loud first, then open the model answer. Interviewers care more about your reasoning than the exact words.
Beginner What is Blob Storage used for?
Model answer
Storing files of any type: pictures, videos, documents, backups and logs. Apps can read and write them over HTTPS from anywhere.
Intermediate Explain the blob access tiers.
Model answer
Hot has the highest storage cost but lowest access cost, for data used often. Cool and Cold are cheaper to store but cost more to read, with minimum storage durations of 30 and 90 days. Archive is the cheapest to store but offline. You must rehydrate it before reading, which can take hours, and it has a 180-day minimum.
Experienced developer How would you automate tiering for logs?
Model answer
Use lifecycle management rules: move blobs to Cool after 30 days without access, to Archive after 180 days, and delete them after the retention period. Watch early-deletion charges and rehydration costs for archived data.
Test yourself with exercises
3 original practice questions in the AZ-900 style. Pick your answers, then check them. You will see why each option is right or wrong. Score 75% or more and this topic is marked complete.
Quick revision
Key points
- Blob Storage = object storage for unstructured data.
- Hot → Cool → Cold → Archive gets cheaper to store and more expensive to access.
- Minimum durations are Cool 30 days, Cold 90 days, Archive 180 days.
- Archive is offline; rehydrate before reading.
- Lifecycle management moves blobs between tiers automatically.
Important terminology
- Blob
- Binary large object. Any file stored in Blob Storage.
- Container
- A folder-like grouping of blobs inside a storage account.
- Access tier
- Hot, Cool, Cold or Archive, which trades storage price against access price.
- Rehydration
- Moving an archived blob back to an online tier so it can be read, which can take hours.
Common mistakes
- Choosing Archive for data that must be read immediately.
Exam tips
- "Cheapest storage, rarely accessed, can wait hours to read" = Archive tier.
Five quick revision questions
-
1.What kind of data is Blob Storage for?Show
Unstructured data such as images, videos, documents and backups.
-
2.Which tier has the lowest storage cost?Show
Archive.
-
3.What is the minimum storage duration for the Cool tier?Show
30 days.
-
4.Can you read Archive data immediately?Show
No. It must be rehydrated first.
-
5.What moves blobs between tiers automatically?Show
Lifecycle management rules.
Official references
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