Many Dell PowerEdge servers have an option to boot select hypervisors from either a single SD card or dual mirrored SD cards. The advantage of this is that the server can be diskless or the local storage is not consumed by the hypervisor. The primary drawback is that SD cards are not meant for continuous writes so only hypervisors that do not routinely write to the OS partition are supported. A second drawback is that reads and writes are slow so it works best for OS’s that are fully load into memory during the boot process.
Dell’s spec sheets for servers are not very explicit in which OS’s can run from the SD card readers. The key term on the spec sheet is “Optional embedded hypervisors” under “Operating systems.” This is generally listed as Citrix XenServer and VMware vSphere ESXI. I have not seen any other OS listed, however, I would look for Windows Nano server to be listed in the future.
Additionally, Dell only supports XenServer only if factory installed by Dell. ESXi is easily installed to the SD card reader by the end user. In the case of ESXi writes only happen when the configuration is changed or updates are done. Also, ESXi fully loads into memory on boot and would not need to read or write unless there is a change. If you want to keep ESXi logs, you must configure ESXi to write logs to a datastore.
It is not recommended to install any other OS or hypervisor to the SD card(s) on a production system. Many other OS’s will continuously write to the OS partition which can quickly wear out the SD card(s). In the case of Windows Server, the installer will refuse to install to the SD card with an error stating that you are not allowed to install to a USB device. While there are ways to bypass this, it is not recommended as Windows will quickly wear out the SD card causing the server to fail.
Installing ESXi on SD Card
Installing VMware vSphere ESXi on the SD card is very straightforward. Dell provides instructions HERE. For best results use the Dell provided ESXi installer media which is linked to in the instructions.