What are Hot, cool, and archive access tiers for blob data?

Data stored in the cloud grows at an exponential pace. To manage costs for your expanding storage needs, it can be helpful to organize your data based on how frequently it will be accessed and how long it will be retained. 

Azure storage offers different access tiers so that you can store your blob data in the most cost-effective manner based on how it is being used. Azure Storage access tiers include:

• Hot tier - An online tier optimized for storing data that is accessed or modified frequently. 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. Data in the cool tier should be stored for a minimum of 30 days. The cool tier has lower storage costs and higher access costs compared to the hot 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. Data in the archive tier should be stored for a minimum of 180 days.

Azure storage capacity limits are set at the account level, rather than according to the access tier. You can choose to maximize your capacity usage in one tier or to distribute capacity across two or more tiers.

Online access tiers

When your data is stored in an online access tier (either hot or cool), users can access it immediately. The hot tier is the best choice for data that is in active use, while the cool tier is ideal for data that is accessed less frequently, but that still must be available for reading and writing.

Example usage scenarios for the hot tier include:

• Data that's in active use or is expected to be read from and written to frequently.
• Data that's staged for processing and eventual migration to the cool access tier.

Usage scenarios for the cool access tier include:

• Short-term data backup and disaster recovery.
• Older data sets that are not used frequently, but are expected to be available for immediate access.
• Large data sets that need to be stored in a cost-effective way while additional data is being gathered for processing.

Data in the cool tier has slightly lower availability, but offers the same high durability, retrieval latency, and throughput characteristics as the hot tier. For data in the cool tier, slightly lower availability and higher access costs may be acceptable trade-offs for lower overall storage costs, as compared to the hot tier. For more information, see SLA for storage.

A blob in the cool tier in a general-purpose v2 accounts is subject to an early deletion penalty if it is deleted or moved to a different tier before 30 days has elapsed. This charge is prorated. 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.

The hot and cool tiers support all redundancy configurations. For more information about data redundancy options in Azure Storage, see Azure Storage redundancy.