A few days ago one of our customers got some brand new BL460c Gen9 systems which will be used as VMware hypervisor hosts. As boot medium a 32GB SD card was configured and built into the internal sd card slot that each ProLiant since G7 offers by default.
During setup the ESXi installer was unable to detect the SD card and thus won't find any suitable target for installation. Hm, quite strange, as we are 100% sure that the SD card was installed and properly detected. Furthermore, we used the latest HP optimized ESXi 5.5 installer ISO, so drivers shouldn't be the problem.
A few minutes searching on the internet revealed a HP advisory that this is probably caused by a bug in the iLO4 firmware and is solved by upgrading to version 2.03. Unfortunately this firmware was already installed and the SD card was shown under possible boot media from the UEFI BIOS.
Just because I had no other idea, I changed from UEFI to legacy BIOS to force the Gen9 systems work like former Gen8 servers and voila, the SD card was detected by the installer. As ESXi 5.5 won't benefit in any way from an UEFI BIOS this isn't a problem at all. We cross checked this behavior on three other hosts (same model, same config, same bladeenclosure) and could reproduce this behavior every time. So it seems, UEFI in combination with the internal SD card reader is a "no-go" config for ESXi 5.5 installations.