Some combinations of option cards can result in failure to load device drivers and subsequent failure to mount file systems or configure network interfaces, and possibly failure to boot the system. This occurs in ESX 4x only.
The ESX host requires "Low Memory," or the memory addressed below 4 GB for the Service Console, device drivers and other data structures. The BIOS utilizes 2 GB of this memory area for its own uses. With the large number of supported I/O devices, this memory can become exhausted in some situations.
VMware describes this problem in their Knowledge Base at https://vmware.com.
Workaround
Use the following procedure to reduce the amount of memory reserved by the Service Console.
Restart the ESX host.
When the boot menu appears, ensure that the default boot option is highlighted.
Press e to edit the default boot option.
A new list appears.
Use the arrow keys to highlight the line that starts with kernel /vmlinuz.
Press the e key to edit the line in the boot configuration.
Use the arrow key to move over the portion of the line which has a parameter similar to the following:
mem=800M
Change the value to 600 megabytes.
For example:
mem=600M
Press Enter to accept the changes.
Press the b key to boot the host using the new configuration.
The configuration is complete but it is not yet permanent.
After the host has booted, open the vSphere Client and connect to the host.
Select the Configuration tab.
Change the memory properties of the ESX host to permanently reduce the RAM assignment.