High Avalibility with Storage Replications

Replication for Durability and High Availability

The data in your Microsoft Azure storage account is always replicated to ensure durability and high availability, meeting the SLA for Storage even in the face of transient hardware failures.

See Azure Regions for more information about what services are available in each region.

When you create a storage account, you must select one of the following replication options:

• Locally redundant storage (LRS). Locally redundant storage maintains three copies of your data. LRS is replicated three times within a single facility in a single region. LRS protects your data from normal hardware failures, but not from the failure of a single facility.
  LRS is offered at a discount. For maximum durability, we recommend that you use geo-redundant storage, described below.
• Zone-redundant storage (ZRS). Zone-redundant storage maintains three copies of your data. ZRS is replicated three times across two to three facilities, either within a single region or across two regions, providing higher durability than LRS. ZRS ensures that your data is durable within a single region.
  ZRS provides a higher level of durability than LRS; however, for maximum durability, we recommend that you use geo-redundant storage, described below.

  Note:

  ZRS is currently available only for block blobs, and is only supported for versions 2014-02-14 and later.

  Once you have created your storage account and selected ZRS, you cannot convert it to use to any other type of replication, or vice versa.
• Geo-redundant storage (GRS). GRS maintains six copies of your data. With GRS, your data is replicated three times within the primary region, and is also replicated three times in a secondary region hundreds of miles away from the primary region, providing the highest level of durability. In the event of a failure at the primary region, Azure Storage will failover to the secondary region. GRS ensures that your data is durable in two separate regions.
  For information about primary and secondary pairings by region, see Azure Regions.
• Read access geo-redundant storage (RA-GRS). Read access geo-redundant storage is enabled for your storage account by default when you create it. Read access geo-redundant storage replicates your data to a secondary geographic location, and also provides read access to your data in the secondary location. Read-access geo-redundant storage allows you to access your data from either the primary or the secondary location, in the event that one location becomes unavailable.

  
  

Understanding Storage Accounts in Azure

General-purpose Storage Accounts

A general-purpose storage account gives you access to Azure Storage services such as Tables, Queues, Files, Blobs and Azure virtual machine disks under a single account. This type of storage account has two performance tiers:

• A standard storage performance tier which allows you to store Tables, Queues, Files, Blobs and Azure virtual machine disks.
• A premium storage performance tier which currently only supports Azure virtual machine disks. See Premium Storage: High-Performance Storage for Azure Virtual Machine Workloads for an in-depth overview of Premium storage.

Blob Storage Accounts

A Blob storage account is a specialized storage account for storing your unstructured data as blobs (objects) in Azure Storage. Blob storage accounts are similar to your existing general-purpose storage accounts and share all the great durability, availability, scalability, and performance features that you use today including 100% API consistency for block blobs and append blobs. For applications requiring only block or append blob storage, we recommend using Blob storage accounts.

Note:

Blob storage accounts support only block and append blobs, and not page blobs.

Blob storage accounts expose the Access Tier attribute which can be specified during account creation and modified later as needed. There are two types of access tiers that can be specified based on your data access pattern:

• A Hot access tier which indicates that the objects in the storage account will be more frequently accessed. This allows you to store data at a lower access cost.
• A Cool access tier which indicates that the objects in the storage account will be less frequently accessed. This allows you to store data at a lower data storage cost.

If there is a change in the usage pattern of your data, you can also switch between these access tiers at any time. Changing the access tier may result in additional charges. Please seePricing and billing for Blob storage accounts for more details.

For more details on Blob storage accounts, see Azure Blob Storage: Cool and Hot tiers.

Before you can create a storage account, you must have an Azure subscription, which is a plan that gives you access to a variety of Azure services. You can get started with Azure with a free account. Once you decide to purchase a subscription plan, you can choose from a variety ofpurchase options. If you’re an MSDN subscriber, you get free monthly credits that you can use with Azure services, including Azure Storage. See Azure Storage Pricing for information on volume pricing.

To learn how to create a storage account, see Create a storage account for more details. You can create up to 100 uniquely named storage accounts with a single subscription. See Azure Storage Scalability and Performance Targets for details about storage account limits.

Storage account billing

You are billed for Azure Storage usage based on your storage account. Storage costs are based on the following factors: region/location, account type, storage capacity, replication scheme, storage transactions, and data egress.

• Region refers to the geographical region in which your account is based.
• Account type refers to whether you are using a general-purpose storage account or a Blob storage account. With a Blob storage account, the access tier also determines the billing model for the account.
• Storage capacity refers to how much of your storage account allotment you are using to store data.
• Replication determines how many copies of your data are maintained at one time, and in what locations.
• Transactions refer to all read and write operations to Azure Storage.
• Data egress refers to data transferred out of an Azure region. When the data in your storage account is accessed by an application that is not running in the same region, you are charged for data egress. (For Azure services, you can take steps to group your data and services in the same data centers to reduce or eliminate data egress charges.)