ASR Replication Policy and Process (Azure-2-Azure)

When you enable Azure VM replication, by default Site Recovery creates a new replication policy with the default settings as below :

Policy setting	Details	Default
Recovery point retention	Specifies how long Site Recovery keeps recovery points	24 hours
App-consistent snapshot frequency	How often Site Recovery takes an app-consistent snapshot.	Every 60 minutes.

* You can modify the default replication policy settings when you enable replication.

Replication Process :

When you enable replication for an Azure VM, the following happens:

1. The Site Recovery Mobility service extension is automatically installed on the VM.
2. The extension registers the VM with Site Recovery.
3. Continuous replication begins for the VM. Disk writes are immediately transferred to the cache storage account in the source location.
4. Site Recovery processes the data in the cache, and sends it to the target storage account, or to the replica managed disks.
5. After the data is processed, crash-consistent recovery points are generated every five minutes. App-consistent recovery points are generated according to the setting specified in the replication policy

Multi-VM Consistency :

If you want VMs to replicate together, and have shared crash-consistent and app-consistent recovery points at failover, you can gather them together into a replication group. Multi-VM consistency impacts workload performance, and should only be used for VMs running workloads that need consistency across all machines.

If you enable multi-VM consistency, machines in the replication group communicate with each other over port 20004.

• Ensure that there is no firewall appliance blocking the internal communication between the VMs over port 20004.
• If you want Linux VMs to be part of a replication group, ensure the outbound traffic on port 20004 is manually opened as per the guidance of the specific Linux version.

Check the crash-consistent and app-consistent recovery points here :

https://pachehra.blogspot.com/2019/06/rp.html

https://pachehra.blogspot.com/2019/06/asrconnreq.html