Unable to see all the HDDs from the BIOS under removable devices

Products

• VMware vSphere ESXi

Issue/Introduction

Cannot see all the disks from in BIOS mode under Boot-> Removable Devices-> Hard Drive

Environment

VMware vSphere vCenter 7.0.x
VMware vSphere vCenter 8.0.x
VMware vSphere ESXi 7.0.x
VMware vSphere ESXi 8.0.x

Cause

• The legacy BIOS firmware relies on INT 13h disk services, a 16-bit interface dating back to DOS-era systems.
• INT 13h only supports a limited number of bootable devices (typically 8 or fewer hard disks)

Resolution

VMware intentionally emulates this to preserve legacy compatibility and the limitation is expected. 

• BIOS mode: Only up to 8 disks are visible to the VM firmware/bootloader.
• UEFI mode: All disks are visible and accessible.

Additional Information

For changing the boot order, please refer the KB: Changing the boot order of a virtual machine on ESXi using virtual machine
Deprecation of legacy BIOS support in vSphere: Compatibility Support Module