Azure Storage Redundancy Options

There are a lot of components that make Azure tick and storage is a big one.  Azure has four types of storage - blobs, files (in preview), table and queue.  Every storage account you create in your subscription has the ability to contain all four types.  In addition to those types, you can pick from four redundancy options:

• Locally Redundant Storage (LRS)
• Zone Redundant Storage (ZRS)
• Geographically Redundant Storage (GRS)
• Read-Access Geographically Redundant Storage (RA-GRS)

Locally Redundant Storage (LRS) is the  cheapest storage option you can select and the end result will be three synchronous copies of your data within a single datacenter.  The SLA offered is 99.9% availability for read and write functions.  LRS is a good choice for data if you have compliance requirement that dictates your data remain in a specific location.

Geographically Redundant Storage (GRS) is the big brother of LRS.  Data is copied three times within a single datacenter, plus multiple asynchronous copies to a second datacenter hundreds of miles away.  This results in six copies of your data.  By default when you create a storage account, it will be GRS.  You can see what secondary location would be used for your redundant copy in the configuration settings of your storage account.  The alternative copy provides protection against a major datacenter outage or disaster, however you don't have control as to when the secondary copy is made available for access.

Read-Access Geographically Redundant Storage (RA-GRS) is the cool twin of GRS.  It’s the same as GRS, but you have the ability to access the secondary datacenter copy for read access whenever you like.  When you activate RA-GRS, you'll be given a second endpoint URL for access to that copy. Because if this, the SLA for read functions increases to 99.99%.

If you create a storage account with any of the three choices above, you can easily change it after the fact within the storage configuration settings. 

Finally, there is Zone Redundant Storage (ZRS).  Similar to LRS, but the three copies of data are stored across multiple datacenters within or across regions.  It's more durable than LRS and more economical than GRS, but is an option for block blobs only. There is no option to change from ZRS storage to the other options and you will see a warning that ZRS if for blob storage only.  Block blobs are used for VM storage as well as documents, videos, backups - any unstructured text or binary data -  but you can't use the same storage account for table or queue storage.  Still this a great option if you are looking for a little extra durability due to outage, but don't need the full on redundancy offered by GRS or RA-GRS.  Storage accounts used for testing purposes would be good use of ZRS.

In addition to these regular "spinning disk" storage options, you can also try out Azure Premium Storage (in Preview). Premium Storage gives you high-performance, low-latency support for I/O workloads running on Azure VMs.  These persistent disks are backed by SSD.  However, you need to have a premium storage account which can only be created using the Preview Portal and it's currently only in limited regions.  Learn more about Premium Storage here.

If you need to know more about the specific pricing for Azure Storage you can visit the pricing page. Your total cost will depend on several factors, not just the redundancy option you pick.  As you look at the hybrid cloud scenarios for storage, you'll find that the cloud won't be the best location for ALL your data, but storing some data in the cloud can be cheaper than expanding storage devices you already own.  Also, if you missed yesterday's series post on Azure Backup Solutions, check it at http://aka.ms/HybridCloudforITPro.