Slow Write Performance to FlexCache Volumes with Autodesk Apps on Azure VMs

Applies to

Issue

Intermittent slow write performance and application freezes when saving files from Autodesk applications (such as AutoCAD) running on Azure VMs to CIFS shares mapped to FlexCache volumes in the same Azure region.
Symptoms include:

• Application freeze or unresponsiveness during file save operations.
• Only a .tmp file is saved; the expected file is not present until the operation completes.
• The issue is most pronounced during write-back to the FlexCache origin volume and is not consistently reproducible.
• Users may bypass FlexCache for direct access to the origin as a workaround.

Example log output:

Performance testing showed write latency for FlexCache volumes (avg ~53ms, 95th percentile >130ms, 99th percentile >360ms), while non-FlexCache volumes had sub-millisecond write latency.