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Azure Migrate Assessment – Internal Error Occurred & Performance Coverage Showing “Not Applicable”

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Azure Migrate – Internal Error ID 951 on Windows Server (AWS → Azure Migration) and Performance Coverage Showing "Not applicable"

Bagavan Muniandy 5 Reputation points
2026-03-04T03:12:51.1633333+00:00

Issue Summary

We are encountering two issues in Azure Migrate:

1. Internal Error – ID 951 (Assessment, Discovery)

During discovery from AWS to Azure, one Windows Server continuously fails with error:

  • Error ID: 951
  • Message: Internal error occurred
  • Affected features: Assessment, Discovery
  • Severity: High

All Linux servers and the other machines in the same discovery group are successfully discovered. Only one Windows Server is failing.

2. Performance Coverage Showing “Not applicable”

Our assessment is performance-based and discovery status shows Ready, with performance metrics visible in the report.

However, the “Performance Coverage” column displays Not applicable, instead of percentage/star rating.

This behaviour is unexpected because:

  • This is a performance-based assessment
  • All machines are appliance-discovered (no CSV import)
  • Discovery has been running long enough
  • All other assessment data is available

Detailed Problem Description

Problem 1 — Internal Error (ID 951) for Windows Server

This issue affects only one Windows Server in AWS during Azure Migrate discovery.

Linux machines are successfully discovered.

Troubleshooting Already Performed

Network / Port Checks

All required ports opened and validated:

443 (Outbound required for server assessment upload)

5985 (WinRM HTTP)

5986 (WinRM HTTPS)

5695 (Azure Migrate appliance → VM)

Verified appliance can reach the VM via private IP and public IP

NSG/firewall rules allow required traffic

VM-side Validation

WinRM service running

WinRM listeners confirmed

Firewall group enabled:

Problem 2 — Performance Coverage = “Not applicable” (Unexpected)

What we expect:

Performance coverage should show:

  • A percentage
  • A star rating (for VM/server assessments)

Current behaviour:

  • Assessment Status = Ready
  • Performance report is visible (metrics exist)
  • However Performance Coverage = Not Applicable

Checks Already Done

  • Assessment type is Performance-based
  • Discovery is Appliance-based (not CSV)
  • Profiling duration is met
  • VMs were powered on during the period
  • CPU/RAM/disk/network data are present
  • Machines were not created midway

Why this is an issue

Based on Microsoft documentation, “Not applicable” is normally shown only when:

  • Assessment is as-is / on-premises, or
  • Assessment uses CSV import, or
  • AVS/VMware cases without utilization

But our scenario does not match any of the above.

This behaviour suggests that:

  • Azure Migrate backend did not assign a performance coverage value, or
  • The internal error (ID 951) is affecting the performance aggregation pipeline for the assessment, or
  • A region-specific backend issue (Malaysia West) is affecting performance coverage computation.

We need Microsoft to verify backend logs.

Problem 2 — Performance Coverage = “Not applicable” (Unexpected)

What we expect:

Performance coverage should show:

  • A percentage
  • A star rating (for VM/server assessments)

Current behaviour:

  • Assessment Status = Ready
  • Performance report is visible (metrics exist)
  • However Performance Coverage = Not Applicable

Checks Already Done

  • Assessment type is Performance-based
  • Discovery is Appliance-based (not CSV)
  • Profiling duration is met
  • VMs were powered on during the period
  • CPU/RAM/disk/network data are present
  • Machines were not created midway

Why this is an issue

Based on Microsoft documentation, “Not applicable” is normally shown only when:

  • Assessment is as-is / on-premises, or
  • Assessment uses CSV import, or
  • AVS/VMware cases without utilization

But our scenario does not match any of the above.

This behaviour suggests that:

  • Azure Migrate backend did not assign a performance coverage value, or
  • The internal error (ID 951) is affecting the performance aggregation pipeline for the assessment, or
  • A region-specific backend issue (Malaysia West) is affecting performance coverage computation.

We need Microsoft to verify backend logs.

What We Need Microsoft to Investigate

For Issue 1: Internal Error ID 951

  • Why only one Windows Server fails discovery while all others (including Linux) succeed
  • Backend logs for this machine’s performance data ingestion
  • Whether this is a known issue for AWS → Azure assessments
  • Whether Azure Migrate appliance logs show data rejection or schema errors
  • Confirmation if this is a region-level or API-level issue

For Issue 2: Performance Coverage “Not applicable”

  • Validate why performance coverage is not calculated despite:
    • VM discovery successful
      • Assessment performance-based
        • All metrics visible
          • No CSV import
          • Confirm if the issue is caused by failed data ingestion (related to ID 951)
  • Check backend processing for the assessment in Malaysia West

    What We Need Microsoft to Investigate

    For Issue 1: Internal Error ID 951

    • Why only one Windows Server fails discovery while all others (including Linux) succeed
    • Backend logs for this machine’s performance data ingestion
    • Whether this is a known issue for AWS → Azure assessments
    • Whether Azure Migrate appliance logs show data rejection or schema errors
    • Confirmation if this is a region-level or API-level issue

    For Issue 2: Performance Coverage “Not applicable”

    • Validate why performance coverage is not calculated despite:
      • VM discovery successful
      • Assessment performance-based
      • All metrics visible
      • No CSV import
    • Confirm if the issue is caused by failed data ingestion (related to ID 951)
    • Check backend processing for the assessment in Malaysia West
Azure Migrate
Azure Migrate

A central hub of Azure cloud migration services and tools to discover, assess, and migrate workloads to the cloud.

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  1. Q&A Assist
    2026-03-04T03:13:14.8433333+00:00
    AI generated content. This question contains an answer created with AI from Q&A Assist. Learn more

    Error 951 and the “Not applicable” performance coverage behavior aren’t documented in the provided Azure Migrate troubleshooting content, and there’s no mapping for error 951 in the common discovery, software inventory, or SQL discovery error tables.

    From the available guidance, the only concrete next step when an internal/unspecified error persists in Azure Migrate discovery or assessment is to open a Microsoft support case and provide appliance and project details so backend logs can be reviewed. The context explicitly recommends this for multiple internal or transient discovery errors (for example, errors 10001, 10003, 9006–9008, 9011, 9032, and several SQL discovery errors), once basic connectivity and credential checks have been completed.

    Given that:

    • Discovery and performance collection are already working for other machines.
    • Network, WinRM, and appliance connectivity have been validated.
    • Error 951 is not listed in the public error catalog.
    • Performance coverage calculation logic and region-specific backend behavior are not exposed in the documentation.

    The supported path is:

    1. Collect Azure Migrate appliance logs and the appliance machine ID from the configuration manager footer.
    2. Collect the Azure Migrate project name, subscription, region (Malaysia West), and the specific assessment name.
    3. Open a Microsoft support case for Azure Migrate, referencing:
      • The internal error ID 951 for the specific Windows Server.
      • The unexpected “Performance coverage = Not applicable” behavior for a performance-based, appliance-discovered assessment with visible metrics.
    4. Provide the collected details so support can inspect backend telemetry and ingestion pipelines for that project/region.

    This aligns with the documented guidance to escalate when discovery or internal errors persist beyond the normal 24‑hour auto-retry window and are not covered by the published error codes.

    References:

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