Storage access tiers
Blob storage accounts use access tiers to determine how frequently data is accessed. Based on this access tier, you will get billed. Azure offers three storage access tiers: Hot, Cool, and Archive. Azure also offers configuration options for blob life cycle management, which we will explore more of in the next chapter.
Hot
The hot access tier is most suitable for storing data that is accessed frequently and data that is in active use. For instance, you would store images and style sheets for a website inside the hot access tier. The storage costs for this tier are higher than for the other access tiers, but you pay less for accessing files. This is the default access tier for storage.
Cool
The cool access tier is the most suitable for storing data that is not accessed frequently (less than once in 30 days). Compared with the hot access tier, the cool tier has lower storage costs, but you pay more for accessing files. This tier is suitable for storing backups and older content that is not viewed often.
Archive
The archive storage tier is set on the blob level and not on the storage level. It has the lowest costs for storing data and the highest cost for accessing data compared to the hot and cool access tiers. This tier is for data that will remain in the archive for at least 180 days, and it will take several hours of latency before it can be accessed. This tier is most suitable for long-term backups or compliance and archive data. A blob in the archive tier is offline and cannot be read (except for the metadata), copied, overwritten, or modified. Although the blob data remains unreadable in the archive tier, its metadata remains readable.
Service-level agreement for storage accounts
It is worth considering the service-level agreement (SLA) for all services when designing and deploying to Azure. The great news with storage accounts is that you are assured of 99% availability of services.
Choosing a cool tier infers a lower SLA from Microsoft, whereas the hot tier allows better SLAs up to 99.99%.
Top Tip
Data tiers can be changed between hot and cool; doing so will charge the full premium at the conversion of the existing storage tier. This charge does not apply to blob storage accounts. Costs are incurred as write operation charges when converting from the hot to the cool tier and as read and data retrieval operations when converting from the cold to the hot tier.
