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You cannot use a manual migration to migrate from ZRS to GZRS or RA-GZRS. You must request a live migration.
Migration from ZRS to GZRS simply isn't available in the Azure portal currently, as the portal makes clear. The below article explains that the account must be migrated with a live migration, unless the change is for a failback operation.
A manual migration can result in application downtime. If your application requires high availability, Microsoft also provides a live migration option. A live migration is an in-place migration with no downtime.
With a manual migration, you copy the data from your existing storage account to a new storage account that uses ZRS in the primary region. To perform a manual migration, you can use one of the following options:
Copy data by using an existing tool such as AzCopy, one of the Azure Storage client libraries, or a reliable third-party tool.
If you're familiar with Hadoop or HDInsight, you can attach both the source storage account and destination storage account account to your cluster. Then, parallelize the data copy process with a tool like DistCp.
Request a live migration to ZRS, GZRS, or RA-GZRS
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