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---
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title: Azure VM Disaster Recovery - High Churn support
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description: Describes how to protect your Azure VMs having high churning workloads.
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title: Azure Virtual Machines disaster recovery - High Churn support
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description: Describes how to protect your Azure Virtual Machines having high churning workloads.
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services: site-recovery
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author: ankitaduttaMSFT
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manager: gaggupta
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ms.service: site-recovery
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ms.topic: conceptual
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ms.date: 03/29/2024
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ms.date: 05/23/2024
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ms.author: ankitadutta
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---
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# Azure VM Disaster Recovery - High Churn Support
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# Azure Virtual Machines disaster recovery - High Churn support
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Azure Site Recovery supports churn (data change rate) up to 100 MB/s per VM. You will be able to protect your Azure VMs having high churning workloads (like databases) using the *High Churn* option in Azure Site Recovery which supports churn up to 100 MB/s per VM. You may be able to achieve better RPO performance for your high churning workloads. With the default Normal Churn option, you can [support churn only up to 54 MB/s per VM](./azure-to-azure-support-matrix.md#limits-and-data-change-rates).
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Azure Site Recovery supports churn (data change rate) up to 100 MB/s per virtual machine. You'll be able to protect your Azure virtual machines having high churning workloads (like databases) using the *High Churn* option in Azure Site Recovery, which supports churn up to 100 MB/s per virtual machine. You may be able to achieve better Recovery Point Objective performance for your high churning workloads. With the default Normal Churn option, you can [support churn only up to 54 MB/s per virtual machine](./azure-to-azure-support-matrix.md#limits-and-data-change-rates).
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## Limitations
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- Available only for DR of Azure VMs.
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- Recommend VM SKUs with RAM of min 32GB.
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- Available only for disaster recovery of Azure virtual machines.
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- Virtual machine SKUs with RAM of min 32 GB are recommended.
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- Source disks must be Managed Disks.
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> [!NOTE]
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- These limits are based on our tests and don't cover all possible application I/O combinations.
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- Actual results may vary based on your app I/O mix.
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- There are two limits to consider:
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- per disk data churn
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- per disk data, churn
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- per virtual machine data churn.
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- Limit per virtual machine data churn - 100 MB/s.
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|Standard or P10 or P15 |8 KB|2 MB/s|
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|Standard or P10 or P15|16 KB|4 MB/s|
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|Standard or P10 or P15|24 KB|6 MB/s|
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|Standard or P10 or P15|32 KB and above|10 MB/s|
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|Standard or P10 or P15|32 KB and later |10 MB/s|
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|P20|8 KB|10 MB/s|
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|P20 |16 KB|20 MB/s|
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|P20|24 KB and above|30 MB/s|
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|P30 and above|8 KB|20 MB/s|
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|P30 and above|16 KB|35 MB/s|
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|P30 and above|24 KB and above|50 MB/s|
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|P20|24 KB and later|30 MB/s|
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|P30 and later|8 KB|20 MB/s|
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|P30 and later|16 KB|35 MB/s|
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|P30 and later|24 KB and later|50 MB/s|
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## How to enable High Churn support
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### From Recovery Service Vault
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1. Select source VMs on which you want to enable replication. To enable replication, follow the steps [here](./azure-to-azure-how-to-enable-replication.md).
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1. Select source virtual machines on which you want to enable replication. To enable replication, follow the steps [here](./azure-to-azure-how-to-enable-replication.md).
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2. Under **Replication Settings** > **Storage**, select **View/edit storage configuration**. The **Customize target settings** page opens.
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:::image type="Replication settings" source="media/concepts-azure-to-azure-high-churn-support/replication-settings-storages.png" alt-text="Screenshot of Replication settings storage." lightbox="media/concepts-azure-to-azure-high-churn-support/replication-settings-storages.png":::
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3. Under **Churn for the VM**, there are two options:
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- **Normal Churn** (this is the default option) - You can get up to 54 MB/s per VM. Select Normal Churn to use *Standard* storage accounts only for Cache Storage. Hence, Cache storage dropdown will list only *Standard* storage accounts.
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- **Normal Churn** (this is the default option) - You can get up to 54 MB/s per virtual machine. Select Normal Churn to use *Standard* storage accounts only for Cache Storage. Hence, Cache storage dropdown lists only *Standard* storage accounts.
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- **High Churn** - You can get up to 100 MB/s per VM. Select High Churn to use *Premium Block Blob* storage accounts only for Cache Storage. Hence, Cache storage dropdown will list only *Premium Block blob* storage accounts.
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- **High Churn** - You can get up to 100 MB/s per virtual machine. Select High Churn to use *Premium Block Blob* storage accounts only for Cache Storage. Hence, Cache storage dropdown lists only *Premium Block blob* storage accounts.
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:::image type="Churn" source="media/concepts-azure-to-azure-high-churn-support/churns.png" alt-text="Screenshot of churn.":::
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:::image type="High churn" source="media/concepts-azure-to-azure-high-churn-support/high-churn-new.png" alt-text="Screenshot of high-churn.":::
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If you select multiple source VMs to configure Site Recovery and want to enable High Churn for all these VMs, select **High Churn** at the top level.
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If you select multiple source virtual machines to configure Site Recovery and want to enable High Churn for all these virtual machines, select **High Churn** at the top level.
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5. After you select High Churn for the VM, you will see Premium Block Blob options only available for cache storage account. Select cache storage account and then select **Confirm Selection**.
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5. After you select High Churn for the virtual machine, you'll see Premium Block Blob options only available for cache storage account. Select cache storage account and then select **Confirm Selection**.
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:::image type="Cache storage" source="media/concepts-azure-to-azure-high-churn-support/cache-storages.png" alt-text="Screenshot of Cache storage.":::
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6. Configure other settings and enable the replication.
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### From Azure VM screen
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### From Azure virtual machine screen
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1. In the portal, go to **Virtual machines** and select the VM.
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1. In the portal, go to **Virtual machines** and select the virtual machine.
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2. On the left pane, under **Operations**, select **Disaster recovery**.
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:::image type="Storage" source="media/concepts-azure-to-azure-high-churn-support/storage-show-details.png" alt-text="Screenshot of Storage show details.":::
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6. Under **Storage settings** > **Churn for the VM**, select **High Churn**. You will be able to use Premium Block Blob type of storage accounts only for cache storage.
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6. Under **Storage settings** > **Churn for the VM**, select **High Churn**. You are able to use Premium Block Blob type of storage accounts only for cache storage.
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:::image type="High churn" source="media/concepts-azure-to-azure-high-churn-support/churn-for-vms.png" alt-text="Screenshot of Churn for VM.":::
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:::image type="High churn" source="media/concepts-azure-to-azure-high-churn-support/churn-for-vms.png" alt-text="Screenshot of Churn for virtual machine.":::
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6. Select **Next: Review + Start replication**.
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>[!Note]
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>- You can only enable High Churn only when you enable replication while configuring Azure Site Recovery on a VM.
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>- If you want to enable High Churn support for VMs already protected by Azure Site Recovery, disable replication for those VMs and select **High Churn** while enabling replication again. Similarly, disable and enable replication again to switch back to **Normal Churn**.
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>- You can only enable High Churn only when you enable replication while configuring Azure Site Recovery on a virtual machine.
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>- If you want to enable High Churn support for virtual machines already protected by Azure Site Recovery, disable replication for those virtual machines and select **High Churn** while enabling replication again. Similarly, disable and enable replication again to switch back to **Normal Churn**.
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## Cost Implications
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- **High Churn** uses *Premium Block Blob* storage accounts which may have higher cost implications as compared to **Normal Churn** which uses *Standard* storage accounts. For more information, see [pricing](https://azure.microsoft.com/pricing/details/storage/blobs/).
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- For High churn VMs, more data changes may get replicated to target for **High churn** compared to **Normal churn**. This may lead to more network cost.
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- **High Churn** uses *Premium Block Blob* storage accounts, which may have higher cost implications as compared to **Normal Churn** which uses *Standard* storage accounts. For more information, see [pricing](https://azure.microsoft.com/pricing/details/storage/blobs/).
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- For High churn virtual machines, more data changes may get replicated to target for **High churn** compared to **Normal churn**. This may lead to more network cost.
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## Next steps
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[Set up disaster recovery for Azure VMs](azure-to-azure-tutorial-enable-replication.md).
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[Set up disaster recovery for Azure virtual machines](azure-to-azure-tutorial-enable-replication.md).

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