NFS fallocate commands failing with vSAN file services

Products

• VMware vSAN

Issue/Introduction

Applications that rely on fallocate calls may need to be adjusted.

Symptoms:
Running Flexible IO tester (FIO) or other applications are failing on NFS mounts provided by vSAN file services.

Environment

VMware vSAN 7.0.x

Cause

The fallocate command is not supported by vSAN file services, so disk space allocation cannot be done by a simple fallocate syscall on NFS mounts.

Resolution

Applications can use a workaround to write to files to allocate required disk space. This may involve multiple syscalls and may not be as fast as fallocate.

In particular, FIO can be run using fallocate=none.