Assessment overview (migrate to Azure VMs)

This article provides an overview of assessments in the Azure Migrate: Discovery and assessment tool. The tool can assess on-premises servers in VMware virtual and Hyper-V environment, and physical servers for migration to Azure.

What's an assessment?

An assessment with the Discovery and assessment tool measures the readiness and estimates the effect of migrating on-premises servers to Azure.

Types of assessments

There are three types of assessments you can create using Azure Migrate: Discovery and assessment.

Assessments you create with Azure Migrate are a point-in-time snapshot of data. An Azure VM assessment provides two sizing criteria options:

How do I run an assessment?

There are a couple of ways to run an assessment.

• Assess servers by using server metadata collected by a lightweight Azure Migrate appliance. The appliance discovers on-premises servers. It then sends server metadata and performance data to Azure Migrate.
• Assess servers by using server metadata that's imported in a comma-separated values (CSV) format.

How do I assess with the appliance?

If you're deploying an Azure Migrate appliance to discover on-premises servers, do the following steps:

1. Set up Azure and your on-premises environment to work with Azure Migrate.
2. For your first assessment, create an Azure project and add the Discovery and assessment tool to it.
3. Deploy a lightweight Azure Migrate appliance. The appliance continuously discovers on-premises servers and sends server metadata and performance data to Azure Migrate. Deploy the appliance as a VM or a physical server. You don't need to install anything on servers that you want to assess.

After the appliance begins server discovery, you can gather servers you want to assess into a group and run an assessment for the group with assessment type Azure VM.

Follow our tutorials for VMware, Hyper-V, or physical servers to try out these steps.

How do I assess with imported data?

If you're assessing servers by using a CSV file, you don't need an appliance. Instead, do the following steps:

1. Set up Azure to work with Azure Migrate
2. For your first assessment, create an Azure project and add the Discovery and assessment tool to it.
3. Download a CSV template and add server data to it.
4. Import the template into Azure Migrate
5. Discover servers added with the import, gather them into a group, and run an assessment for the group with assessment type Azure VM.

What data does the appliance collect?

If you're using the Azure Migrate appliance for assessment, learn about the metadata and performance data that's collected for VMware and Hyper-V.

How does the appliance calculate performance data?

If you use the appliance for discovery, it collects performance data for compute settings with these steps:

1. The appliance collects a real-time sample point.

   • VMware VMs: A sample point is collected every 20 seconds.
   • Hyper-V VMs: A sample point is collected every 30 seconds.
   • Physical servers: A sample point is collected every five minutes.

2. The appliance combines the sample points to create a single data point every 10 minutes for VMware and Hyper-V servers, and every 5 minutes for physical servers. To create the data point, the appliance selects the peak values from all samples. It then sends the data point to Azure.

3. The assessment stores all the 10-minute data points for the last month.

4. When you create an assessment, the assessment identifies the appropriate data point to use for rightsizing. Identification is based on the percentile values for performance history and percentile utilization.

   • For example, if the performance history is one week and the percentile utilization is the 95th percentile, the assessment sorts the 10-minute sample points for the last week. It sorts them in ascending order and picks the 95th percentile value for rightsizing.
   • The 95th percentile value makes sure you ignore any outliers, which might be included if you picked the 99th percentile.
   • If you want to pick the peak usage for the period and don't want to miss any outliers, select the 99th percentile for percentile utilization.

5. This value is multiplied by the comfort factor to get the effective performance utilization data for these metrics that the appliance collects:

   • CPU utilization
   • RAM utilization
   • Disk IOPS (read and write)
   • Disk throughput (read and write)
   • Network throughput (in and out)

How are Azure VM assessments calculated?

The assessment uses the on-premises servers' metadata and performance data to calculate assessments. If you deploy the Azure Migrate appliance, assessment uses the data the appliance collects. But if you run an assessment imported using a CSV file, you provide the metadata for the calculation.

Calculations occur in these three stages:

1. Calculate Azure readiness: Assess whether servers are suitable for migration to Azure.
2. Calculate sizing recommendations: Estimate compute, storage, and network sizing.
3. Calculate monthly costs: Calculate the estimated monthly compute, storage, and security costs for running the servers in Azure after migration.

Calculations are in the preceding order. A server moves to a later stage only if it passes the previous one. For example, if a server fails the Azure readiness stage, it's marked as unsuitable for Azure. Sizing and cost calculations aren't done for that server.

What's in an Azure VM assessment?

Here's what's included in an Azure VM assessment:

Review the best practices for creating an assessment with Azure Migrate.

Calculate readiness

Not all servers are suitable to run in Azure. An Azure VM Assessment assesses all on-premises servers and assigns them a readiness category.

• Ready for Azure: The server can be migrated as-is to Azure without any changes. It will start in Azure with full Azure support.
• Conditionally ready for Azure: The server might start in Azure but might not have full Azure support. For example, Azure doesn't support a server that's running an old version of Windows Server. You must be careful before you migrate these servers to Azure. To fix any readiness problems, follow the remediation guidance the assessment suggests.
• Not ready for Azure: The server won't start in Azure. For example, if an on-premises server's disk stores more than 64 TB, Azure can't host the server. Follow the remediation guidance to fix the problem before migration.
• Readiness unknown: Azure Migrate can't determine the readiness of the server because of insufficient metadata.

To calculate readiness, the assessment reviews the server properties and operating system settings summarized in the following tables.

Server properties

For an Azure VM Assessment, the assessment reviews the following properties of an on-premises VM to determine whether it can run on Azure VMs.

Guest operating system

For an Azure VM Assessment, along with reviewing VM properties, the assessment looks at the guest operating system of a server to determine whether it can run on Azure.

The assessment uses the following logic to identify Azure readiness based on the operating system:

Security readiness

Assessments also determine readiness of the recommended target for Microsoft Defender for Servers. A server is marked as Ready for Microsoft Defender for Servers if it has the following:

• Minimum 2 vCores (4 vCores preferred)
• Minimum 1 GB RAM (4 GB preferred)
• 2 GB of disk space
• Runs any of the following Operating Systems:
  • Windows Server 2008 R2, 2012 R2, 2016, 2019, 2022
  • Red Hat Enterprise Linux Server 7.2+, 8+, 9+
  • Ubuntu 16.04, 18.04, 20.04, 22.04
  • SUSE Linux Enterprise Server 12, 15+
  • Debian 9, 10, 11
  • Oracle Linux 7.2+, 8
  • CentOS Linux 7.2+
  • Amazon Linux 2
• For other Operating Systems, the server is marked as Ready with Conditions. If a server is not ready to be migrated to Azure, it is marked as Not Ready for Microsoft Defender for Servers.

Calculating sizing

After the server is marked as ready for Azure, the assessment makes sizing recommendations in the Azure VM assessment. These recommendations identify the Azure VM and disk SKU. Sizing calculations depend on whether you're using as-is on-premises sizing or performance-based sizing.

Calculate sizing (as-is on-premises)

If you use as-is on-premises sizing, the assessment doesn't consider the performance history of the VMs and disks in the Azure VM assessment.

• Compute sizing: The assessment allocates an Azure VM SKU based on the size allocated on-premises.
• Storage and disk sizing: The assessment looks at the storage type specified in assessment properties and recommends the appropriate disk type. Possible storage types are Standard HDD, Standard SSD, Premium, and Ultra disk. The default storage type is Premium.
• Network sizing: The assessment considers the network adapter on the on-premises server.

Calculate sizing (performance-based)

If you use performance-based sizing in an Azure VM assessment, the assessment makes sizing recommendations as follows:

• The assessment considers the performance (resource utilization) history of the server along with the processor benchmark to identify the VM size and disk type in Azure.

• This method is especially helpful if you've overallocated the on-premises server, utilization is low, and you want to right-size the Azure VM to save costs.
• If you don't want to use the performance data, reset the sizing criteria to as-is on-premises, as described in the previous section.

Calculate storage sizing

For storage sizing in an Azure VM assessment, Azure Migrate tries to map each disk that is attached to the server to an Azure disk. Sizing works as follows:

1. Assessment adds the read and write IOPS of a disk to get the total IOPS required. Similarly, it adds the read and write throughput values to get the total throughput of each disk. In the case of import-based assessments, you have the option to provide the total IOPS, total throughput and total no. of disks in the imported file without specifying individual disk settings. If you do this, individual disk sizing is skipped and the supplied data is used directly to compute sizing, and select an appropriate VM SKU.

2. Disks are selected as follows:

   • If assessment can't find a disk with the required IOPS and throughput, it marks the server as unsuitable for Azure.
   • If assessment finds a set of suitable disks, it selects the disks that support the location specified in the assessment settings.
   • If there are multiple eligible disks, assessment selects the disk with the lowest cost.
   • If performance data for any disk is unavailable, the configuration disk size is used to find a Standard SSD disk in Azure.

Ultra disk sizing

For Ultra disks, there is a range of IOPS and throughput that is allowed for a particular disk size, and thus the logic used in sizing is different from Standard and Premium disks:

1. Three Ultra disk sizes are calculated:
   • One disk (Disk 1) is found that can satisfy the disk size requirement
   • One disk (Disk 2) is found that can satisfy total IOPS requirement
     • IOPS to be provisioned = (source disk throughput) *1024/256
   • One disk (Disk 3) is found that can satisfy total throughput requirement
2. Out of the three disks, one with the max disk size is found and is rounded up to the next available Ultra disk offering. This is the provisioned Ultra disk size.
3. Provisioned IOPS is calculated using the following logic:
   • If source throughput discovered is in the allowable range for the Ultra disk size, provisioned IOPS is equal to source disk IOPS
   • Else, provisioned IOPS is calculated using IOPS to be provisioned = (source disk throughput) *1024/256
4. Provisioned throughput range is dependent on provisioned IOPS

Calculate network sizing

For an Azure VM assessment, assessment tries to find an Azure VM that supports the number and required performance of network adapters attached to the on-premises server.

• To get the effective network performance of the on-premises server, assessment aggregates the data transmission rate out of the server (network out) across all network adapters. It then applies the comfort factor. It uses the resulting value to find an Azure VM that can support the required network performance.
• Along with network performance, assessment also considers whether the Azure VM can support the required number of network adapters.
• If network performance data is unavailable, assessment considers only the network adapter count for VM sizing.

Calculate compute sizing

After it calculates storage and network requirements, the assessment considers CPU and RAM requirements to find a suitable VM size in Azure.

• Azure Migrate looks at the effective utilized cores (including processor benchmark) and RAM to find a suitable Azure VM size.
• If no suitable size is found, the server is marked as unsuitable for Azure.
• If a suitable size is found, Azure Migrate applies the storage and networking calculations. It then applies location and pricing-tier settings for the final VM size recommendation.
• If there are multiple eligible Azure VM sizes, the one with the lowest cost is recommended.

Confidence ratings (performance-based)

Each performance-based Azure VM assessment in Azure Migrate is associated with a confidence rating. The rating ranges from one (lowest) to five (highest) stars. The confidence rating helps you estimate the reliability of the size recommendations Azure Migrate provides.

• The confidence rating is assigned to an assessment. The rating is based on the availability of data points that are needed to compute the assessment.
• For performance-based sizing, the assessment needs:
  • The utilization data for CPU and RAM.
  • The disk IOPS and throughput data for every disk attached to the server.
  • The network I/O to handle performance-based sizing for each network adapter attached to a server.

If any of these utilization numbers isn't available, the size recommendations might be unreliable.

Ratings

This table shows the assessment confidence ratings, which depend on the percentage of available data points:

Low confidence ratings

Here are a few reasons why an assessment could get a low confidence rating:

• You didn't profile your environment for the duration for which you're creating the assessment. For example, if you create the assessment with performance duration set to one day, you must wait at least a day after you start discovery for all the data points to get collected.

• Assessment is not able to collect the performance data for some or all the servers in the assessment period. For a high confidence rating, ensure that:

  • Servers are powered on for the duration of the assessment
  • Outbound connections on ports 443 are allowed
  • For Hyper-V servers, dynamic memory is enabled

  Recalculate the assessment to reflect the latest changes in confidence rating.

• Some servers were created during the time for which the assessment was calculated. For example, assume you created an assessment for the performance history of the last month, but some servers were created only a week ago. In this case, the performance data for the new servers will not be available for the entire duration and the confidence rating would be low.

Calculate monthly costs

After sizing recommendations are complete, an Azure VM assessment in Azure Migrate calculates compute and storage costs for after migration.

Compute cost

Azure Migrate uses the recommended Azure VM size and the Azure Billing API to calculate the monthly cost for the server.

The calculation takes into account the:

• Operating system
• Software assurance
• Reserved instances
• VM uptime
• Location
• Currency settings

The assessment aggregates the cost across all servers to calculate the total monthly compute cost.

Storage cost

The monthly storage cost for a server is calculated by aggregating the monthly cost of all disks that are attached to the server.

Standard and Premium disk

The cost for Standard or Premium disks is calculated based on the selected/recommended disk size.

Ultra disk

The cost for Ultra disk is calculated based on the provisioned size, provisioned IOPS and provisioned throughput. Learn more

Cost is calculated using the following logic:

• Cost of disk size is calculated by multiplying provisioned disk size by hourly price of disk capacity
• Cost of provisioned IOPS is calculated by multiplying provisioned IOPS by hourly provisioned IOPS price
• Cost of provisioned throughput is calculated by multiplying provisioned throughput by hourly provisioned throughput price
• The Ultra disk VM reservation fee is not added in the total cost. Learn More

Assessment calculates the total monthly storage costs by aggregating the storage costs of all servers. Currently, the calculation doesn't consider offers specified in the assessment settings.

Security cost

For servers recommended for Azure VM, if they're ready to run Defender for Server, the Defender for Server cost (Plan 2) per server for that region is added. The assessment aggregates the cost across all servers to calculate the total monthly security cost.

Costs are displayed in the currency specified in the assessment settings.

Next steps

Review best practices for creating assessments.

• Learn about running assessments for servers running in VMware and Hyper-V environment, and physical servers.
• Learn about assessing servers imported with a CSV file.
• Learn about setting up dependency visualization.