Choose the right storage access tiers for your blob data

Storage tier comparison

❑ Background

With massive explosion of different types of data in the form of images, logs, sensors, videos, texts, and documents, Companies are face enormous challenge around managing the scale of this data in a cost-efficient manner. Each of these data have different characteristics. Some are actively accessed and modified throughout its lifetime while some of these data are accessed frequently early in its lifetime, with access dropping drastically as the data ages. Some of these data remains idle in the cloud and is rarely, if ever, accessed after it’s stored.

To accommodate these different access needs, Azure provides several access tiers, which you can use to balance your storage costs with your access needs. It is important to plan & organize your data based on how long it will be retained & on how frequently it will be accessed.

I have observed many organizations using these tiers effectively to save lots of storage cost and get maximum value out of cloud storage. In this quick bite, we will go through the different storage tiers in Azure & scenarios to use these tiers effectively.

❑ Different storage access tiers

Azure Storage access tiers include:

Hot tier — An online tier optimized for storing data that’s in active use or is expected to be accessed and modified frequently. e.g., Static files for web pages.

  • The Hot tier has the highest storage costs, but the lowest access costs.

Cool tier — An online tier optimized for storing data that is infrequently accessed or modified. e.g., Short-term data backup and disaster recovery.

  • Data in the Cool tier has slightly lower availability, but offers the same high durability, retrieval latency, and throughput characteristics as the Hot tier.
  • The Cool tier has lower storage costs and higher access costs compared to the Hot tier.
  • General-purpose v2 accounts have a minimum retention duration of 30 days for cool tier. For Blob Storage accounts, there’s no minimum retention duration for the Cool tier.
  • A blob in the Cool tier in a general-purpose v2 account is subject to an early deletion penalty if it’s deleted or moved to a different tier before 30 days has elapsed.
  • Early Deletion penalty is on Pro-rata basis — For example, if a blob is moved to the Cool tier and then deleted after 21 days, you’ll be charged an early deletion fee equivalent to 9 (30 minus 21) days of storing that blob in the Cool tier.

Archive tier — An offline tier optimized for storing data that is rarely accessed, and that has flexible latency requirements, on the order of hours. e.g., Long-term backup, secondary backup, and archival datasets stored for Compliance reason (Call center audio call logs).

  • Data in the Archive tier should be stored for a minimum of 180 days or be subject to an early deletion charge. The Cool tier has lower storage costs and higher access costs compared to the Hot & Cool tier.
  • A blob can’t be read or modified while a blob is in the Archive tier.
  • To read or download a blob in the Archive tier, you must first rehydrate it to an online tier, either Hot or Cool. Data in the Archive tier can take up to 15 hours to rehydrate, depending on the priority (standard or high rehydration) you specify for the rehydration operation.
  • Early Deletion/penalty is on Pro-rata basis. For example, if a blob is moved to the Archive tier and then deleted or moved to the Hot tier after 45 days, the customer is charged an early deletion fee for 135 (180 minus 45) days of storage in the Archive tier.

The account access tier is the default tier that is inferred by any blob without an explicitly set tier. You can set default tier only as Hot or Cool.

❒ Setting or changing a blob’s tier

After a blob is created, you can change its tier in either of the following ways:

➊ Calling the Set Blob Tier operation, either directly or via a lifecycle management policy. Calling Set Blob Tier is typically the best option when you’re changing a blob’s tier from a hotter tier to a cooler one.

➋ Calling the Copy Blob operation to copy a blob from one tier to another. Calling Copy Blob is recommended for most scenarios where you’re rehydrating a blob from the Archive tier to an online tier or moving a blob from Cool to Hot.

By copying a blob, you can avoid the early deletion penalty, if the required storage interval for the source blob hasn’t yet elapsed. However, copying a blob result in capacity charges for two blobs, the source blob and the destination blob.

❑ Indicative Pricing*

Data Storage price

Key Observation — Storage price is cheaper for cool & Archive tier

Operation & Data transfer cost

Key Observation — Read & Write Operation price for Hot tier is cheaper than cool & Archive tier.

*Please note that this pricing is just indicative taken at time of writing this blog, but the actual pricing depends on various other factors. Please refer Azure Storage Blobs Pricing | Microsoft Azure & Pricing Calculator | Microsoft Azure for arriving at pricing for your storage.

Important Points to Note

  • As we move from hot -> cool -> archive the cost of storage goes down but the cost of transactions increases.
  • The archive access tier can only be set at the blob level and not on the account.
  • Hot, cool, and archive tiers can be set at the blob level, during upload or after upload.
  • New Storage Accounts are created in the Hot Tier by default.
  • Please refer for more information of pricing and Billing for blob access tiers
  • Changing a blob’s tier from Hot to Cool or Archive & Cool to Hot is instantaneous. Rehydrating a blob from the Archive tier to either the Hot or Cool tier can take up to 15 hours.

❑ Reference

Hot, Cool, and Archive access tiers for blob data — Azure Storage | Microsoft Docs

Rehydrate an archived blob to an online tier — Azure Storage | Microsoft Docs

I hope this blog helped you in understanding various storage tier options in Azure & choosing Azure destination tier for your data.

Till then, Happy Learning!!!

Please Note — All opinions expressed here are my personal views and not of my employer.

Thought of the moment-

Alone we can do so little; together we can do so much - Helen Keller -



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RK Iyer

RK Iyer

Architect@Microsoft, Technology Evangelist, Sports Enthusiast! All opinions here are my personal thoughts and not my employers.