The Sun Server X4-4 defaults in BIOS to 64-bit MMIO (Memory Mapped I/O). This allows additional PCIe memory address space to be mapped above the standard 32-bit 4GB of space for PCIe cards that include option ROMs. However, VMware ESXi is incompatible with MMIO space above the standard 4GB. This issue can cause some PCIe cards not to function properly with ESXi.
Workaround
As a possible workaround, disable 64-bit MMIO through the server's BIOS Setup Utility (under the IO > PCIe Subsystem Settings > PCI 64-bit Resources Allocation menu). This workaround has limitations. With some combinations of option cards, the system will require more MMIO space than what the system can allocate within 32 bits of address space. When that occurs, those option cards that could not be assigned MMIO address space (because there was not enough left) will be unavailable for use.
For more information, refer to VMware's Knowledge Base at: