VCF Download Tool binaries download fails with checksum mismatch and AVX-512 incompatibility

Products

• VMware Cloud Foundation

Issue/Introduction

VCF Download Tool experiencing systemic data corruption during downloads. The issue is rooted in an incompatibility between AVX-512 instruction handling and vSAN versions 8.0, 8.0U1, or 8.0U2, leading to checksum mismatch.

Environment

VMware vSAN 8.0, 8.0U1, and 8.0U2.

VMware Cloud Foundation

VCF Download Tool

Cause

Applications may leverage Intel or AMD AVX-512 instructions to accelerate checksum operations. However, a compatibility conflict arises when these 512-bit instructions interact with the underlying vSAN storage subsystem, which operates on standard AVX/AVX2 logic. By restricting applications to standard AVX/AVX2 instructions, we eliminate the high-level register conflicts triggered by AVX-512. This fallback mechanism provides a reliable workaround, as the 256-bit instruction path is natively stable within the vSAN infrastructure.

Resolution

This issue is fixed in ESXi 8.0U3 It’s strongly recommended to use vSAN 8.0U3 or later.

Additional Information

To ensure data integrity when an immediate upgrade is not feasible, the recommended workaround is to disable or fallback to lower-level AVX instructions at the application level. By restricting the use of AVX-512, the system defaults to stable 256-bit instruction sets that do not experience this integrity issue.

Workaround 1: Disable AVX-512 instructions through vCenter

1. Go to the vCenter and find the VM you want to disable AVX-512.

2. Power Off the VM.

3. Add the following two settings in the VM advanced options (VM Hardware → Edit → Advanced Parameters)

Attribute: featMask.vm.cpuid.AVX512F Value: Max:0
Attribute: featMask.vm.cpuid.AVX512FP16 Value: Max:0

4. Power On the VM.

Workaround 2: Fallback to lower-level AVX instructions:

1. Execute the following line in the terminal before executing VCF download tool:

export JAVA_TOOL_OPTIONS="-XX:UseAVX=2"

Related KB : Applications using AVX-512 instructions in vSAN 8.0/8.0U1/8.0U2 may report data inconsistency issues