Unable to retrieve per-disk metrics from DCR to Log Analytics for Azure VM disk space monitoring

Question

Unable to retrieve per-disk metrics from DCR to Log Analytics for Azure VM disk space monitoring

Hitul Gala 40

Dear Microsoft Support Team,

We are currently facing an issue with Azure Monitor Data Collection Rules (DCR) related to disk performance metrics collection for our Azure Virtual Machines.

Requirement: Our objective is to configure alerting for disk space utilization such that an alert is triggered when free space falls below 10% per disk, per virtual machine.

Issue Description: We have configured a Data Collection Rule (DCR) using Azure Monitor Agent (AMA) to collect the following performance counter:

\LogicalDisk(*)% Free Space

The DCR is successfully associated with the target virtual machines and is correctly pointing to the designated Log Analytics Workspace. However, when querying the Perf table in Log Analytics, we are only receiving records with:

ObjectName: LogicalDisk

CounterName: % Free Space (and Free Megabytes)

InstanceName: _Total

We are not receiving individual disk instances (e.g., C:, D:, etc.), which prevents us from implementing per-disk alerting.

Could you please assist with the following:

Confirm whether per-instance LogicalDisk metrics are fully supported via AMA and DCR.

Advise if there are additional configuration steps required to enable per-disk data collection.

Confirm whether there are known limitations or agent-side issues affecting LogicalDisk instance collection.

This functionality is critical for implementing disk space threshold alerts at <10% free space per disk per VM.

Please let us know if you require any further details to assist with troubleshooting.

Hitul Gala 40 Reputation points

2026-02-26T06:49:51.55+00:00

Hello Bharath,

Thank you for the response!
As checked, we are using the correct performance counter: \LogicalDisk(*)\% Free Space , there seems to be a typo in the above question.

Also, the given query for InsightsMetrics does not give any output if run at the log analytics workspace. Would request you to connect over a call to check the issue further.
Bharath Y P 10,610 Reputation points Microsoft External Staff Moderator

2026-02-26T22:16:45.61+00:00

Hello Hitul Gala, We are investigating this issue, we will update you on this. thanks

Bharath Y P 10,610 Microsoft External Staff Moderator

As Discussed, please use the below query to get the VM disk instances with the percent of free space.

Perf
| where ObjectName == "LogicalDisk"
| where CounterName in ("% Free Space", "Free Megabytes")
| summarize LatestRecord = arg_max(TimeGenerated, CounterValue)
    by Computer, InstanceName, CounterName
| evaluate pivot(CounterName, take_any(CounterValue))
| extend FreeSpacePercent = todouble(["% Free Space"])
| extend FreeSpaceMB = todouble(["Free Megabytes"])
| extend TotalDiskMB = iif(FreeSpacePercent > 0, FreeSpaceMB * 100.0 / FreeSpacePercent, 0.0)
| extend UsedSpaceMB = TotalDiskMB - FreeSpaceMB
| project Computer, InstanceName, FreeSpacePercent

Bharath Y P 10,610 Reputation points Microsoft External Staff Moderator

2026-03-05T09:50:48.6266667+00:00

Hello Hitul Gala, I just wanted to kindly follow up to check, If the provided Query is worked for you, if you have any further question, please let us know. Thanks
Rajesh Kumar Gantekampu 0 Reputation points

2026-07-16T10:18:14.8466667+00:00

I think the ask is per disk not per vm free space, if i am not wrong, can we get per disk in a vm free space

Answer accepted by question author

Bharath Y P 10,610 Microsoft External Staff Moderator

Hello Hitul Gala,You have configured Azure Monitor Agent (AMA) with a Data Collection Rule (DCR) to collect disk free space metrics using the performance counter: \LogicalDisk(*)% Free Space. The DCR is correctly associated with the target virtual machines, Pointing to the intended Log Analytics Workspace and Successfully ingesting data into the Perf table. However, the collected data not Individual disk instances (for example C:, D:) are not present, which blocks your requirement to configure per‑disk alerts when free space falls below 10% per VM.

Generally, you should ensure that your DCR configuration is correct. Double-check that you are using the correct performance counter: \LogicalDisk(*)\% Free Space and \LogicalDisk(*)\Free Megabytes If configured properly, it should capture metrics for each disk instance.

You can try to update Windows performance counters follow a strict path format like \LogicalDisk(*)\% Free Space and \LogicalDisk(*)\Free Megabytes See if this works.

Collect performance counters with Azure Monitor Agent - Azure Monitor | Azure Docs

After updating as per the above format, Validate your query in the Log Analytics workspace. You can use the provided KQL queries to ensure that metrics are correctly collected. For example, you can modify queries for the perf table to focus specifically on each disk's free space:

Perf
| where ObjectName == "LogicalDisk"
| where CounterName in ("% Free Space", "Free Megabytes")
| summarize LatestRecord = arg_max(TimeGenerated, CounterValue)
    by Computer, InstanceName, CounterName
| evaluate pivot(CounterName, take_any(CounterValue))
| extend FreeSpacePercent = todouble(["% Free Space"])
| extend FreeSpaceMB = todouble(["Free Megabytes"])
| extend TotalDiskMB = iif(FreeSpacePercent > 0, FreeSpaceMB * 100.0 / FreeSpacePercent, 0.0)
| extend UsedSpaceMB = TotalDiskMB - FreeSpaceMB
| project Computer, InstanceName, FreeSpacePercent

Hope this helps. and please feel free to reach out if you have any further questions. Thanks

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Hitul Gala 40 Reputation points

2026-02-26T06:49:51.55+00:00

Hello Bharath,

Thank you for the response!
As checked, we are using the correct performance counter: \LogicalDisk(*)\% Free Space , there seems to be a typo in the above question.

Also, the given query for InsightsMetrics does not give any output if run at the log analytics workspace. Would request you to connect over a call to check the issue further.
Bharath Y P 10,610 Reputation points Microsoft External Staff Moderator

2026-02-26T22:16:45.61+00:00

Hello Hitul Gala, We are investigating this issue, we will update you on this. thanks
Bharath Y P 10,610 Reputation points Microsoft External Staff Moderator

2026-03-04T09:34:21.57+00:00

As Discussed, please use the below query to get the VM disk instances with the percent of free space.

Perf | where ObjectName == "LogicalDisk" | where CounterName in ("% Free Space", "Free Megabytes") | summarize LatestRecord = arg_max(TimeGenerated, CounterValue) by Computer, InstanceName, CounterName | evaluate pivot(CounterName, take_any(CounterValue)) | extend FreeSpacePercent = todouble(["% Free Space"]) | extend FreeSpaceMB = todouble(["Free Megabytes"]) | extend TotalDiskMB = iif(FreeSpacePercent > 0, FreeSpaceMB * 100.0 / FreeSpacePercent, 0.0) | extend UsedSpaceMB = TotalDiskMB - FreeSpaceMB | project Computer, InstanceName, FreeSpacePercent
Bharath Y P 10,610 Reputation points Microsoft External Staff Moderator

2026-03-05T09:50:48.6266667+00:00

Hello Hitul Gala, I just wanted to kindly follow up to check, If the provided Query is worked for you, if you have any further question, please let us know. Thanks
Rajesh Kumar Gantekampu 0 Reputation points

2026-07-16T10:18:14.8466667+00:00

I think the ask is per disk not per vm free space, if i am not wrong, can we get per disk in a vm free space

Answer 1

Hitul Gala 40

Hello Bharath,

I had to manually add the performance counter \LogicalDisk(*)\% Free Space in the DCR, post which the data started flowing into the Log Analytics Workspace. Similarly, I added \LogicalDisk(*)\Free Megabytes in the DCR and the given query worked.

Thank you!

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