#SaveTheData 2: Secondary Redundancy – how the cloud stretches across regions to keep your data safer

#SaveTheData is a blog series in which we explore how the cloud handles redundancy in Microsoft Azure. The concept of redundancy is pretty simple: your data is important and you don’t want to lose important things or face downtime- so let’s have several sets of the same data exist in multiple places. The cloud offers several redundancy options that, if implemented correctly, allow full backups of your data ready to be restored in case the worst happens.

If you missed part 1, we explored how Azure handles primary redundancy. As a quick recap, primary redundancy allows data to be redundant within a single Azure region such as France Central. Within that region, it can be redundant within the same Azure availability zone (Locally Redundant Storage) or multiple availability zones (Zone Redundant Storage). 

This week we are upping the situation to secondary redundancy. This is when we have data redundancy across regions and in this way protects against large geographical disasters. There are also two forms of redundancy here. Azure determines what the secondary region pairs are for each region and therefore takes care of this for us.

Geo-redundant Storage

Geo-redundant storage is when besides the 3 local copies of the data, it is also copied to the secondary region. The local copies are done at the same time, also known as synchronously. The copy of the data to the secondary region is done when the local copies are completed, also known as asynchronously. 

Once your data has reached one of the locations in the secondary region, data is copied synchously to 3 locations in the secondary region. This means that there are a total of 6 copies of your data

Geo-zone-redundant Storage

We can go up another level to Geo-zone-redundant storage. This is where the data is first copied across 3 Availability Zones in the primary region, this is done synchronously. Then the data is copied asynchronously to a single location in the secondary region where it is again copied synchronously 3 times.

In this scenario, there are also 6 copies of your data, with the first 3 in various availability zones. 

Bringing it all together

Locally redundant storage (LRS) – 3 copies in 1 availability zone

Zone redundant storage (ZRS) – 3 copies across 3 availability zones

Geo-redundant Storage (GSR) – 6 copies, 3 in 1 availability zone in region 1, 3 in 1 availability zone in region 2

Geo-zone-redundant Storage (GZRS) 6 copies, 3 across 3 availability zones in region 1, 3 across 3 availability zones in region 2

These are the 4 ways in which Microsoft Azure tackles Data Redundancy. Next week we will further expand on some Redundancy facts and include advice on some best practices that could be useful for your applications.

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