Trying to boot off an NVMe drive on older hardware can cause some issues. If you are running an older BIOS/UEFI, it may not have the needed drivers to understand how to talk to a NVMe drive. I ran into this exact issue when trying to boot my Dell R510 from an NVMe drive.

To boot from NVMe, I would need to use some shim which could be booted by the BIOS which would chain-boot the actual OS on the NVMe.

Attempt 1 - Clover

The first method I attempted to used was the Clover Bootloader. Clover, while primarily used for Hackintoshes, can have NVMe support added and chain boot to another disk. I wanted to try this first as I would prefer an OS-indifferent solution that would continue to work no matter what I installed on the NVMe.

I attempted to image Clover onto a USB drive and after several wrong attempts, I finally formatted the USB as fat32 and just copy/pasted the contents to the drive. I then followed instructions I found to enable NVMe compatibility by copying NvmExpressDxe.efi from EFI/CLOVER/drivers/off into EFI/CLOVER/drivers/BIOS/ and EFI/CLOVER/drivers/UEFI/. I then modified the EFI/CLOVER/config.plist file to automatically boot the the NVMe drive after a 5 second pause.

However, I could never get Clover to read this config.plist file. I tried placing it in other paths that were suggested by comments on the internet. I tried reverting to the original file and modifying one small value to ensure I had not messed up the file formatting. Still, I could not get Clover to read the config file and automatically boot from the NVMe drive. It would just remain at the boot selection menu where I could manually select the NVMe to boot from which would then work perfectly.

Attempt 2 - Proxmox Boot

Proxmox comes with the proxmox-boot-tool tool which is used to synchronize all the boot disks with the UEFI (ESP) partition. After giving up on Clover, I looked into proxmox-boot-tool and found I could just place an extra ESP partition on the USB drive and let proxmox-boot-tool keep it up-to-date and synced.

Rather than creating the correct partitions in the correct locations and of the right size, I just did a dd if=/dev/<root pool> of=/dev/<usb drive> bs=1M count=1024 to copy over the first 1 GB of the disk. I then used gparted to delete the main partition (leaving the BIO and ESP partitions) and to give the remaining partitions new UUIDs. I then booted into Proxmox and proxmox-boot-tool format /dev/disk/by-uuid/<USB ESP partition UUID> --force and proxmox-boot-tool init /dev/disk/by-uuid/<USB ESP partition UUID>. Once that finished, I rebooted and the USB drive was used as the boot drive which booted into the main Proxmox OS.

Conclusion

I’ve had this in place for a few months now and it has worked perfectly through several updates to the boot cmdline options and kernel updates.