Separate VM limits from disk limits
Azure VM sizes have limits for IOPS and throughput, while individual disks have their own performance characteristics. The effective workload limit can be constrained by either side of the path.
Identify the affected disk
Map the application volume to its Azure managed disk and operating-system device. Confirm whether the issue affects one disk or the entire VM.
Measure the workload
Look at read/write IOPS, throughput and latency together. A workload can hit an IOPS ceiling without reaching a throughput ceiling, or the reverse.
Check the VM size
If the VM size has lower storage bandwidth than the disks can provide, changing only the disk type may not solve the problem. Compare the workload requirement with the VM and disk limits.
Check application behavior
Large sequential transfers and small random I/O have different performance profiles. Review database settings, backup jobs, antivirus activity and scheduled scans that may change the workload during the incident.
Validate after changes
Capture the same performance counters before and after the change. This gives you evidence that the bottleneck moved or was removed.
Useful commands
Get-PhysicalDisk
Get-Counter '\LogicalDisk(*)\Avg. Disk sec/Read'
Get-Counter '\LogicalDisk(*)\Avg. Disk sec/Write'What good troubleshooting looks like
Use evidence before configuration changes. Record the symptom, test result, change made and validation result so another engineer can repeat the procedure.
Symptom → hypothesis → direct test → controlled change → validation → documentation
Frequently asked questions
What should I check first?
Start with the exact failed path or dependency and test it directly before changing configuration.
Should I change production configuration immediately?
No. Capture the current state first and make one controlled change at a time.
How should I document the fix?
Record the symptom, commands, result, configuration change and validation result.
Related TechRunbook guides
Primary reference
This guide was independently written for TechRunbook. Technical details were checked against current Microsoft documentation. Microsoft Learn reference →
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