RA copy availability during and after failover

Vrazo, Tim 2 Reputation points
2021-12-20T20:32:38.687+00:00

if I have an RA-GRS storage account, is the RA copy of an RA-GRS storage account available during failover? How about after?

Azure Storage Accounts
Azure Storage Accounts
Globally unique resources that provide access to data management services and serve as the parent namespace for the services.
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  1. Sumarigo-MSFT 47,476 Reputation points Microsoft Employee
    2021-12-21T06:40:03.707+00:00

    @Vrazo, Tim For better understanding the issue: Can you please elaborate bit more your query? May I know what exactly are you trying to accomplish?

    The failover occurs from the storage account's primary cluster to secondary cluster for (RA-)GRS/GZRS accounts. The secondary cluster will become primary after failover. For more information, please refer to https://learn.microsoft.com/azure/storage/common/storage-disaster-recovery-guidance.

    Additional information: Geo-redundant storage (GRS) or geo-zone-redundant storage (GZRS) copies your data asynchronously in two geographic regions that are at least hundreds of miles apart. If the primary region suffers an outage, then the secondary region serves as a redundant source for your data. You can initiate a failover to transform the secondary endpoint into the primary endpoint.

    Read-access geo-redundant storage (RA-GRS) or read-access geo-zone-redundant storage (RA-GZRS) provides geo-redundant storage with the additional benefit of read access to the secondary endpoint. If an outage occurs in the primary endpoint, applications configured for read access to the secondary and designed for high availability can continue to read from the secondary endpoint. Microsoft recommends RA-GZRS for maximum availability and durability for your applications

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    Initiate a storage account failover: https://learn.microsoft.com/en-us/azure/storage/common/storage-initiate-account-failover?tabs=azure-portal

    Looking forward for your reply!

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  2. Sumarigo-MSFT 47,476 Reputation points Microsoft Employee
    2022-01-03T10:28:41.27+00:00

    @ Azure Files does not support read-access geo-redundant storage (RA-GRS) and read-access geo-zone-redundant storage (RA-GZRS).

    If datacenter level failover happens, then RA-GRS will help to read data in case of disaster. if it is RA-GRS enabled for storage account , then data will sync between primary to secondary

    If your storage account is configured for read access to the secondary region, then you can design your applications to seamlessly shift to reading data from the secondary region if the primary region becomes unavailable for any reason.

    The secondary region is available for read access after you enable RA-GRS or RA-GZRS, so that you can test your application in advance to make sure that it will properly read from the secondary in the event of an outage. For more information about how to design your applications to take advantage of geo-redundancy, see Use geo-redundancy to design highly available applications.

    When read access to the secondary is enabled, your application can be read from the secondary endpoint as well as from the primary endpoint. The secondary endpoint appends the suffix –secondary to the account name. For example, if your primary endpoint for Blob storage is myaccount.blob.core.windows.net, then the secondary endpoint is myaccount-secondary.blob.core.windows.net. The account access keys for your storage account are the same for both the primary and secondary endpoints.

    For more information, please refer to this article: https://learn.microsoft.com/en-us/azure/storage/common/geo-redundant-design?tabs=current

    Azure Storage redundancy: https://learn.microsoft.com/en-us/azure/storage/common/storage-redundancy

    After a failover, the storage account will stay in the secondary region as the new primary storage endpoint but all existing URIs will work the same before and after a geo-failover since the DNS entry of your storage account account..core.windows.net would be updated to point from the primary location to the secondary location. I think if the original primary region is back online, it will probably be the new secondary region for the data geo redundant. You can refer to the comments in the blog. It will depend on the issue. The options we have are to failover the primary, or to restore data on the primary from the secondary and our choice would depend on the issue at hand.

    What is the Geo-Failover Process? Geo failover is the process of configuring a storage account’s secondary location as the new primary location. At present, failover is at stamp level and we do not have the ability to failover a single storage account. We plan to provide an API to allow customers to trigger a failover at an account level, but this is not available yet. Given that failover is at the stamp level, in the event of a major disaster that affects the primary location, we will first try to restore the data in the primary location. Restoring of primary is given precedence since failing over to secondary may result in recent delta changes being lost because of the nature of replication being asynchronous, and not all applications may prefer failing over if the availability to the primary can be restored.

    If we needed to perform a failover, affected customers will be notified via their subscription contact information. As part of the failover, the customer’s “account..core.windows.net” DNS entry would be updated to point from the primary location to the secondary location. Once this DNS change is propagated, the existing Blob, Table, and Queue URIs will work. This means that you do not need to change your application’s URIs – all existing URIs will work the same before and after a geo-failover. For example, if the primary location for a storage account “myaccount” was North Central US, then the DNS entry for myaccount..core.windows.net would direct traffic to North Central US. If a geo-failover became necessary, the DNS entry for myaccount..core.windows.net would be updated so that it would then direct all traffic for the storage account to South Central US. After the failover occurs, the location that is accepting traffic is considered the new primary location for the storage account. Once the new primary is up and accepting traffic, we will bootstrap to a new secondary to get the data geo redundant again.

    Please let us know if you have any further queries. I’m happy to assist you further.

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