Microsoft Azure LRS vs ZRS vs GRS

On the Azure platform, the terms LRS, ZRS and GRS are used in a wide variety of situations. Often, however, their meaning seems to receive too little attention or is disregarded entirely. Especially when it comes to availability, security and Service-Level Agreements (SLA) as such. For this reason, this blog post deals with the meaning and the essential differences.

Redundancies of the Azure storage system

Basically, the designations refer to different redundancies of the Azure storage. Azure essentially differentiates between storage in the same Azure region and storage across regions. The following table provides an overview and will be described in more detail later in this article.

ShortNameRedundancy
LRSLocal redundant storageStores data synchronously three times at one physical location.
ZRSZone redundant storageStores data synchronously three times at three physical locations in the same region.
GRSGeo redundant storageSaves the data synchronously three times at the primary physical location (LRS) and asynchronously three times in a secondary physical region.

The table does not include all available options (such as RA-GRS / Read-access-GRS), but is limited to the three fundamental options. In the following, these three options are described in more detail and graphically displayed to aid understanding.

Local redundant storage (LRS)

As shown in the table, with this option the data is stored three times synchronously in one physical location. This means that the data is also bound to this location. Basically, such a "physical location" is called a "zone" and can be thought of as a building, data center or part of it.

A zone is defined by having its own network infrastructure as well as a supply of electricity, climate, etc. So if this zone suffers a complete failure (e.g. fire), the data is affected despite redundancy, because it shares the same "single point of failure" . This creates the risk that the data can no longer be recovered and is therefore lost.

The LRS option is the most performant, but also the one with the least security. So you should consider how critical your data is and if this option is the right one for a productive environment

Zone redundant storage (ZRS)

The table above states that Azure stores data at ZRS synchronously three times distributed over three physical locations in the same region.  Compared to LRS, this option therefore breaks out of the individual zone and is enhanced with additional zones in the same region.

This significantly increases safety. If a single physical location (zone) experiences a total failure and another zone in the same region remains undamaged, data availability is still guaranteed. However, if the entire region (e.g. Switzerland North) experiences a total failure, even zone-redundant storage does not protect against loss.

Geo redundant storage (GRS)

If the zone-redundant storage is not sufficient for the requirements, the geo redundant storage (GRS) is available as a further option. With this option, Azure itself breaks down the region boundary and accesses another region in which Microsoft stores the data again. As a result, the data is synchronously available three times in a zone of the primary region, as is the case with LRS. In addition, however, an asynchronous copy of the data finds its way into a single zone of the second (secondary) region, thus providing increased protection.

Two or more regions together each form a geography, with the regions at least 300 miles apart, if possible. Typically, a geography consists of markets or national borders, such as Switzerland. There the two regions "Switzerland North" and "Switzerland" West form the geography "Switzerland". The data do not leave the geography.

Differences of the Service Level Agreement (SLA)

The redundancy of the data is certainly a very important factor and should not be ignored. But to make a well-founded decision on the type to be selected, other factors must also be taken into account. In addition to redundancy, geography, costs and, of course, performance, the Service Level Agreement (SLA) is also a decisive factor, as is the case with all offers purchased as a service. Depending on which storage type is chosen (Cool and Hot), Microsoft guarantees a different SLA. The same guaranteed availability applies to Azure LRS, ZRS and GRS.

 Hot StorageCool Storage
LRS99.9%99%
ZRS99.9%99%
GRS99.9%99%
*The SLA applies per calendar month

So if you consider only the storage isolated from other services, the choice of the redundancy type is not important. The more decisive factor is whether Hot or Cool storage is used. But to make the best decision it is important that you also inform yourself about the SLAs of the other used and possibly dependent services.


Sources:
https://docs.microsoft.com/en-us/azure/storage/common/storage-redundancy
https://azure.microsoft.com/en-us/global-infrastructure/regions/
https://azure.microsoft.com/en-us/support/legal/sla/storage/v1_5/

2 thoughts on “Microsoft Azure LRS vs ZRS vs GRS”

  1. Hi Yannic,

    Thanks for this article !!!

    You may want to add the GZRS and RA-GZRS which are new.

    Best regards
    Nicolas

    Reply
    • Hello Nicolas,

      Thank you a lot for your comment. In a first stage I’ll focus on mainly on the basic 3 options, as RA is generally just additional read access on the copies. But fair point, GZRS in fact is a very interesting one, which I should add in a second version of this article. Thank you for your valuable feedback, I’ll let you know as soon as it’s done.

      Best,
      Yannic

      Reply

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