Storage redundancy options

Natasha Ong
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4 min read

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In a nutshell:

Redundancy options are vital for storage safety, offering backup copies in case of failures or disasters.
There are six redundancy options in Azure, each with unique characteristics and considerations, from synchronous data replication to different levels of durability and accessibility.
Redundancy can occur in the primary region (LRS and ZRS) and extend to a secondary region for extra protection (GRS and GZRS), with read-access options for immediate data retrieval in the secondary region (RA-GRS and RA-GZRS).

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When you create a storage account, you get to choose the type of account you want to create, and this choice you make shapes how your data is stored and managed.

Each type has its unique strengths and use cases - let's learn 'em in this guide.

Redundancy options

Remember how we picked Locally-redundant storage in our blob storage activity? Here's our chance to really understand what each of these options mean.

What does redundancy mean? Redundancy means having multiple copies or backups of your data in different places, like secret hideouts. This makes sure your stuff is safe and available even if unexpected events like hardware failures, power outages, or natural disasters strike.

There are six types of redundancy options:

  • Locally redundant storage (LRS)
  • Geo-redundant storage (GRS)
  • Zone-redundant storage (ZRS)
  • Geo-zone-redundant storage (GZRS)
  • Read-access geo-redundant storage (RA-GRS)
  • Read-access geo-zone-redundant storage (RA-GZRS)

When deciding which redundancy option is best for your scenario, consider their differences in costs and availability. The key words to watch out for are:

  • Synchronous: Synchronous means data is instantly copied to another place as it's created, like a real-time backup. Asynchronous means data is copied with a slight delay, so it may not be up-to-date at all times.
  • Durability: Durability looks at how well your data is protected and how likely it will available even in case of problems. "Nines of durability" is a popular way of measuring how reliable and long-lasting your data storage is. More nines = greater reliability. For example, if we say a redundancy option has "11 nines of durability," it means there is a 99.999999999% (eleven nines) probability that your data will be accessible and protected from damage over the course of a year. For most customers, they'll never lose anything stored on Azure with such good promises of durability!
  • Failover: Failover is like a backup plan - it kicks in if your primary storage spot has issues and switch things over to your backup to keep things running. A manual failover means the person looking after your Azure storage accounts will have to flip the switch themselves (so it's not done automatically).

Redundancy in the primary region

This setting means data in your storage account is always replicated three times in the primary region.

Azure Storage offers two options for how your data is replicated in the primary region:

Locally Redundant Storage (LRS)

This option creates three copies of your data within a single data centre. It's cost-effective but offers the least durability. If a disaster such as fire or flooding occurs within the data centre, all replicas of a storage account using LRS may be lost or unrecoverable.

Zone-Redundant Storage (ZRS)

This option goes further and replicates your data in synchronously across three availability zones in the primary region, offering higher durability and accessibility. Microsoft recommends using ZRS in the primary region for scenarios that require high availability. ZRS is also recommended for restricting replication of data within a country or region, to meet some governments' data protection rules.

Redundancy in a secondary region

For an extra layer of protection, your data can be copied to a region far, far away from the primary one, protecting against catastrophic failures across an entire region. When you create a storage account, the second secondary region is based on Azure Region Pairs and can't be changed.

Geo-Redundant Storage (GRS)

This guardian synchronously makes three copies your data within the primary region and then asynchronously to a secondary region. It's like having LRS in two regions.

Because data is replicated to the secondary region asynchronously, a failure that affects the primary region may result in data loss if the data hasn't copied over to the secondary region yet. Recovery point objective (RPO) measures the time it takes for data in the secondary region to update when there are changes in the primary region. Azure Storage typically has an RPO of less than 15 minutes.

Geo-Zone-Redundant Storage (GZRS)

Data in a GZRS storage account is copied across three Azure availability zones in the primary region (similar to ZRS) and is also replicated to a secondary geographic region, using LRS, for protection from regional disasters. Microsoft recommends using GZRS for applications requiring maximum consistency, durability, and availability, excellent performance, and resilience for disaster recovery.

Read Access

So you've learnt that geo-redundant storage means data is copies over to a secondary region. A big to know about this is the copies data in your secondary region is unavailable for you to access until it's needed - i.e. until a big disaster happens and it's not available in your primary region anymore.

That's where these two options come in:

  • Read-access geo-redundant storage (RA-GRS)
  • Read-access geo-zone-redundant storage (RA-GZRS)

Enabling read access means that your data in the secondary region is always available for you to read, even when the primary region is working fine.

Here's the final comparison!

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