Azure Zone Redundant Storage

Q: What is Azure Zone Redundant Storage?

A: There are several different types of storage offerings in Azure. The most common are:

  • Locally Redundant Storage (LRS): Three copies of the data are maintained within a single Azure data center.
  • Geo Redundant Storage (GRS): Similar to LRS, with three copies of data within an Azure data center; however, the data is also asynchronously replicated to the paired Azure data center hundreds of miles away, where the storage is replicated three times, resulting in six total copies of the data.

Zone Redundant Storage (ZRS) provides a middle option between LRS and GRS. Most Azure regions have more than one data center; this is leveraged by ZRS to split the three copies of the data across multiple facilities within the region (although in some instances the data could be split over two regions), with two of the facilities at least 25 miles apart. ZRS currently supports only block BLOBs. This provides storage resiliency greater than LRS because the data is spread over more than one data center. Data is synchronously replicated when the multiple data centers are within a region; in the event that multiple regions are needed, three copies are synchronously stored within the region and data is asynchronously replicated to facilities in other regions.

Note that you can't change the type of a storage account; therefore, you need to ensure that you get the zone type correct during creation.

If you're wondering about the order of resiliency, you can think of it as GRS > ZRS > LRS. GRS is the most resilient, then ZRS, and lastly LRS.

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