Cloud Computing

Working With Azure Cool Storage

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Microsoft recently announced the general availability of Cool Blob Storage in Azure, a new more affordable way to archive files in the cloud. In this post, I’ll explain what Cool Storage is, what Hot Storage is, how they are priced, how to deploy Cool Storage, and what you’ll see in the Azure Portal.

What is Cool Storage?

Microsoft received a lot of feedback to further reduce the cost of storage in the cloud, particularly for data that is rarely accessed but must be retained for operational, legal, or regulatory reasons. Microsoft responding by creating a new tier of Block Blob storage in Azure.

Remember, according to Microsoft, Block Blob storage is:

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… used for streaming and storing documents, videos, pictures, backups, and other unstructured text or binary data.

Now there are two kinds of Block Blob storage accounts:

  • Hot: The kind that we used before, with a 99.9% SLA.
  • Cool: A more affordable storage account for archival purposes, normally with a 99% SLA.

Creating a Cool Storage Account

When you create a new ARM storage account in the Azure Portal at, and not in the classic management portal, you get a new experience. You will be asked if you want to create a “Blob storage” account or a “General purpose” storage account.

Creating a new cool Blob Storage account in Azure [Image Credit: Aidan Finn]
Creating a new cool Blob Storage account in Azure [Image Credit: Aidan Finn]
If you select “Blob storage” then you will select an Access Tier for the storage account, Hot or Cool, and this will affect the pricing of the new storage account.

Replication can have one of three values:

  • Locally-redundant storage (LRS).
  • Geo-redundant storage (GRS).
  • Read-access geo-redundant storage (RA-GRS) – note the SLA of cool storage is increased to 99.9%.

Zone redundant storage (ZRS) is not an option for Block Blob storage accounts.

Note the Performance/Access Tier of the cool storage account [Image Credit: Aidan Finn]
Note the Performance/Access Tier of the cool storage account [Image Credit: Aidan Finn]

Modifying a Storage Account

You cannot modify the hot/cool status of any storage account that was:

  • Created previous to the GA of cool storage
  • Deployed as a general purpose storage account

Note that you can see the configuration of storage account in the management portal. There are three storage accounts in the below screenshot:

  • hottamale: A general purpose storage account, with a performance/access tier description of “Standard”.
  • joecool: A cool Block Blob storage account.
  • pertridc: A storage account that was created before the release of hot/cool Block Blob storage, with a performance/access tier description of “Standard”.

Viewing the hot/cool/general purpose storage accounts in Azure [Image Credit: Aidan Finn]
Viewing the hot/cool/general purpose storage accounts in Azure [Image Credit: Aidan Finn]
Of the above, only the Block Blob storage account (BlobStorage) can be switched from cool to hot, or vice versa. You can do this by opening the settings of the storage account, browsing to Configuration, and changing the Access Tier setting from Cool to Hot, or vice versa.

Modifying the access tier of an Azure hot/cool Block Blob storage account [Image Credit: Aidan Finn]
Modifying the access tier of an Azure hot/cool Block Blob storage account [Image Credit: Aidan Finn]


You can find the pricing for your desired region, currency and resiliency/replication types of hot/cool storage at the recently updated Azure storage pricing page. In North Europe (Ireland):

  • Cool LRS storage starts at $0.01 or €0.0084 per GB/month.
  • Hot LRS storage starts at $0.024 or €0.0202 per GB/month.

If cool storage is so much cheaper then why wouldn’t you use it for storing all of your blobs? The answer lies in how Microsoft describes the use case for cool storage:

In general, any data which lives for a longer period of time and is accessed less than once a month is a perfect candidate for cool storage.

Note the phrase “accessed less than once a month”. This is real archive data, so Microsoft has tuned the pricing of hot versus cold based on your rate of access. Hot storage is more expensive to keep, but cheaper to access than cold storage. For example, in North Europe the pricing of data retrieval (per GB) is:

  • $0.01 or €0.0084 for cool storage.
  • Free for hot storage.

So the choice is simple:

  • If you will rarely access your blobs, put them in cool storage.
  • If you will regularly access your blobs, put them in hot storage.

Usage Scenarios

The obvious case you might want to use is Azure Backup; unfortunately Azure Backup does not support cool storage at this time, but you can vote to change this at the official feedback site.

Developers can modify their software to use cool storage with very little effort; the APIs are unchanged. Some third-party software already can take advantage of the storage option, but I would advise caution on the choice of cool versus hot storage based on the required access rate of the blobs:

  • Commvault for backup.
  • Veritas NetBackup.
  • SoftNAS (coming soon) for hybrid storage.
  • Chosesity for hybrid storage, archival, and replication.
  • CloudBerry Backup, for service provider-focused online backup.

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Aidan Finn, Microsoft Most Valuable Professional (MVP), has been working in IT since 1996. He has worked as a consultant and administrator for the likes of Innofactor Norway, Amdahl DMR, Fujitsu, Barclays and Hypo Real Estate Bank International where he dealt with large and complex IT infrastructures and MicroWarehouse Ltd. where he worked with Microsoft partners in the small/medium business space.
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