Monitor free disk space on Azure VM

This is not possible today through Azure Portal or Azure Monitor. Free disk space is a guest OS performance counter. If this is a Windows VM, you can use the Windows Azure Diagnostics (WAD) agent to collect performance counters to either Azure Storage table and/or EventHub and setup custom tool to monitor this data. If this is a Linux VM, there is also the equivalent Linux Diagnostic Extension.

Here are some relevant links on WAD -

https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-windows-extensions-diagnostics-template?toc=%2fazure%2fvirtual-machines%2fwindows%2ftoc.json https://docs.microsoft.com/en-us/azure/monitoring-and-diagnostics/azure-diagnostics-streaming-event-hubs

Update 2019

This is possible today. To monitor free disk space per drive with Azure Monitor do the following:

1. Enable Guest Operating System OS Metrics for the VM.
2. In the Azure Portal select the Virtual Machine.
3. Click Diagnostics Settings (under Monitoring).
4. Click the Performance counters tab.
5. Click the Custom button.
6. In the textbox add the custom metric for the drive you would like. e.g. \LogicalDisk(C:)\% Free Space.
7. Click Add and set the Unit to Percent.

Source: Azure Support.

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To view the logs from the Azure Guest Monitor for Linux:

// Virtual Machine free disk space
// Show the latest report of free disk space, per instance
InsightsMetrics
| where Name == "FreeSpacePercentage"
| summarize arg_max(TimeGenerated, *) by Tags
// arg_max over TimeGenerated returns the latest record
| project TimeGenerated, Computer, Val, Tags

This results in the following alert query (you need AggregatedValue and bin(TimeGenerated, <some time>) in the query):

InsightsMetrics
| where Name == "FreeSpacePercentage"
| summarize AggregatedValue=arg_min(Val, *)  by bin(TimeGenerated, 5min), Tags

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To view the same for any generic diagnostics endpoint (thanks @gabe):

After turning this on, i was able to view the free disk space with a log query:

// Virtual Machine free disk space 
// Show the latest report of free disk space, per instance 
Perf 
 | where ObjectName == "LogicalDisk" or 
// the object name used in Windows records 
  ObjectName == "Logical Disk" // the object name used in Linux records 
 | where CounterName == "Free Megabytes" 
 | summarize arg_max(TimeGenerated, *) by InstanceName 
// arg_max over TimeGenerated returns the latest record 
 | project TimeGenerated, InstanceName, CounterValue

For now, it is not possible on Azure Portal.

But you could do it by using Azure OMS. There is a example how to use Azure OMS to monitor free disk.