Merge pull request #110129 from Rajeswari-Mamilla/master

Update vmware-azure-architecture.md

Author: PMEds28

articles/site-recovery/vmware-azure-architecture.md

@@ -20,7 +20,7 @@ The following table and graphic provide a high-level view of the components used
 
 **Component** | **Requirement** | **Details**
 --- | --- | ---
-**Azure** | An Azure subscription, Azure Storage account for cache, Managed Disk and Azure network. | Replicated data from on-premises VMs is stored in Azure storage. Azure VMs are created with the replicated data when you run a failover from on-premises to Azure. The Azure VMs connect to the Azure virtual network when they're created.
+**Azure** | An Azure subscription, Azure Storage account for cache, Managed Disk, and Azure network. | Replicated data from on-premises VMs is stored in Azure storage. Azure VMs are created with the replicated data when you run a failover from on-premises to Azure. The Azure VMs connect to the Azure virtual network when they're created.
 **Configuration server machine** | A single on-premises machine. We recommend that you run it as a VMware VM that can be deployed from a downloaded OVF template.<br/><br/> The machine runs all on-premises Site Recovery components, which include the configuration server, process server, and master target server. | **Configuration server**: Coordinates communications between on-premises and Azure, and manages data replication.<br/><br/> **Process server**: Installed by default on the configuration server. It receives replication data; optimizes it with caching, compression, and encryption; and sends it to Azure Storage. The process server also installs Azure Site Recovery Mobility Service on VMs you want to replicate, and performs automatic discovery of on-premises machines. As your deployment grows, you can add additional, separate process servers to handle larger volumes of replication traffic.<br/><br/> **Master target server**: Installed by default on the configuration server. It handles replication data during failback from Azure. For large deployments, you can add an additional, separate master target server for failback.
 **VMware servers** | VMware VMs are hosted on on-premises vSphere ESXi servers. We recommend a vCenter server to manage the hosts. | During Site Recovery deployment, you add VMware servers to the Recovery Services vault.
 **Replicated machines** | Mobility Service is installed on each VMware VM that you replicate. | We recommend that you allow automatic installation from the process server. Alternatively, you can install the service manually or use an automated deployment method, such as Configuration Manager.
@@ -30,33 +30,41 @@ The following table and graphic provide a high-level view of the components used
 ![Components](./media/vmware-azure-architecture/arch-enhanced.png)
 
 
-
 ## Replication process
 
 1. When you enable replication for a VM, initial replication to Azure storage begins, using the specified replication policy. Note the following:
     - For VMware VMs, replication is block-level, near-continuous, using the Mobility service agent running on the VM.
     - Any replication policy settings are applied:
         - **RPO threshold**. This setting does not affect replication. It helps with monitoring. An event is raised, and optionally an email sent, if the current RPO exceeds the threshold limit that you specify.
         - **Recovery point retention**. This setting specifies how far back in time you want to go when a disruption occurs. Maximum retention on premium storage is 24 hours. On standard storage it's 72 hours. 
-        - **App-consistent snapshots**. App-consistent snapshot can be take every 1 to 12 hours, depending on your app needs. Snapshots are standard Azure blob snapshots. The Mobility agent running on a VM requests a VSS snapshot in accordance with this setting, and bookmarks that point-in-time as an application consistent point in the replication stream.
+        - **App-consistent snapshots**. App-consistent snapshot can be taken every 1 to 12 hours, depending on your app needs. Snapshots are standard Azure blob snapshots. The Mobility agent running on a VM requests a VSS snapshot in accordance with this setting, and bookmarks that point-in-time as an application consistent point in the replication stream.
 
 2. Traffic replicates to Azure storage public endpoints over the internet. Alternately, you can use Azure ExpressRoute with [Microsoft peering](../expressroute/expressroute-circuit-peerings.md#microsoftpeering). Replicating traffic over a site-to-site virtual private network (VPN) from an on-premises site to Azure isn't supported.
-3. After initial replication finishes, replication of delta changes to Azure begins. Tracked changes for a machine are sent to the process server.
+3. Initial replication operation ensures that entire data on the machine at the time of enable replication is sent to Azure. After initial replication finishes, replication of delta changes to Azure begins. Tracked changes for a machine are sent to the process server.
 4. Communication happens as follows:
 
     - VMs communicate with the on-premises configuration server on port HTTPS 443 inbound, for replication management.
     - The configuration server orchestrates replication with Azure over port HTTPS 443 outbound.
     - VMs send replication data to the process server (running on the configuration server machine) on port HTTPS 9443 inbound. This port can be modified.
-    - The process server receives replication data, optimizes and encrypts it, and sends it to Azure storage over port 443 outbound.
+    - The process server receives replication data, optimizes, and encrypts it, and sends it to Azure storage over port 443 outbound.
 5. The replication data logs first land in a cache storage account in Azure. These logs are processed and the data is stored in an Azure Managed Disk (called as asr seed disk). The recovery points are created on this disk.
 
-
-
-
 **VMware to Azure replication process**
 
 ![Replication process](./media/vmware-azure-architecture/v2a-architecture-henry.png)
 
+## Resynchronization process
+
+1. At times, during initial replication or while transferring delta changes, there can be network connectivity issues between source machine to process server or between process server to Azure. Either of these can lead to failures in data transfer to Azure momentarily.
+2. To avoid data integrity issues, and minimize data transfer costs, Site Recovery marks a machine for resynchronization.
+3. A machine can also be marked for resynchronization in situations like following to maintain consistency of between source machine and data stored in Azure
+    - If a machine undergoes force shut-down
+    - If a machine undergoes configurational changes like disk resizing (modifying the size of disk from 2 TB to 4 TB)
+4. Resynchronization sends only delta data to Azure. Data transfer between on-premises and Azure by minimized by computing checksums of data between source machine and data stored in Azure.
+5. By default resynchronization is scheduled to run automatically outside office hours. If you don't want to wait for default resynchronization outside hours, you can resynchronize a VM manually. To do this, go to Azure portal, select the VM > **Resynchronize**.
+6. If default resynchronization fails outside office hours and a manual intervention is required, then an error is generated on the specific machine in Azure portal. You can resolve the error and trigger the resynchronization manually.
+7. After completion of resynchronization, replication of delta changes will resume.
+
 ## Failover and failback process
 
 After replication is set up and you run a disaster recovery drill (test failover) to check that everything's working as expected, you can run failover and failback as you need to.