The Azure Migrate Server Assessment tool is used for assessing your on-premises infrastructure. It can assess Hyper-V VMs, VMware VMs, and physical servers. It can help you identify the following:

• Azure readiness: It can help you define whether your on-premises machines are ready for migration to Azure. It scans the OS of the VM to assess whether your on-premises machines are ready for migration to Azure. The VMs that are assessed can be added to the following categories:
  • Ready for Azure: The machine is up-to-date and can be migrated as-is to Azure without any changes. It will start in Azure with full Azure support.
  • Conditionally ready for Azure: Machines in this category might start in Azure but might not have full Azure support. This can be the case for machines that run an older version of Windows Server that isn't supported in Azure. It's recommended that you follow the remediation guidance that is suggested in the assessment to fix these issues. 
  • Not ready for Azure: Machines in this category will not start in Azure. For instance, you might have a machine with a disk of more than 64 TB attached to it. These disks cannot be hosted in Azure. For these machines, it is also recommended to follow the remediation guidance and fix the issues that appear before they are migrated. Note that for the machines in this category, right-sizing and cost estimation is not done.  
  • Readiness unknown: Azure Migrate wasn't able to determine the readiness of the machine because of insufficient metadata that was collected from the on-premises environment.
• Azure sizing: Based on historical data, such as the growth of the disks of the VM, Azure Migrate can estimate the size of Azure VMs after migration.
• Azure cost estimation: Azure Migrate can also estimate the costs for running your on-premises servers in Azure.
• Dependency visualization: When dependency visualization is enabled, Azure Migrate is capable of visualizing cross-server dependencies, and it will also provide you with optimal ways to move dependent servers to Azure.

Before you can execute a server assessment, a lightweight appliance needs to be installed on the on-premises environment. Then, the appliance needs to be registered with the server assessment tool in Azure. This appliance does the following:

• It discovers the on-premises machines in your current environment.
• It connects to the server assessment and sends machine metadata and performance data to Azure Migrate.
• The appliance discovery process is completely agentless; it doesn't require anything to be installed on the discovered machines.
• Discovered machines can be placed into groups. Typically, you place machines into groups that you want to migrate to the same batch.
• For each group, you can create an assessment. You can figure out your migration strategy by analyzing the different assessments.