I just got a CM4 donated with 1GB main memory, 32GB eMMC and 128 GB NVMe. Thank you very much to the donator!
CM4 was already supported by raspiBackup but only running from a SD card, eMMC or USB boot. It's already possible to use NVMe when it's provided in an USB plug because it's exposed as a normal disk as /dev/sdx but there was no way to use a NVMe plugged in in the PCI lane exposed as /dev/nvme. Now I fortunately was able to add this support to raspiBackup. This support is available in a the inofficial release 0.6.7.1 and is planned to be officially available in the next release of raspiBackup.
How to make the CM4 NVMe device available on Linux to restore a NVMe backup created with raspiBackup
If you want to restore an NVMe backup you have to mount the NVMe device on a Linux system in the following way:
Here are full instructions (Sourced from: https://jamesachambers.com/full-compute-module-4-raspberry-pi-setup-imaging-guide/ combined with the mass-storage-gadget documentation on github):
Disconnect power from the CM4 carrier board, and change the USB boot switch behind the HDMI port to "ON"
Connect a USB cable from your other Pi/Linux computer to the CM4 Carrier's USB-C port
Open terminal on your linux computer and run the following to set up rpiboot/usbboot:
sudo apt install git libusb-1.0-0-dev build-essential
git clone --depth=1 https://github.com/raspberrypi/usbboot
sudo make install
Then to mount the drives:
sudo ../rpiboot -d .
Once done the boot and rootfs partitions of eMMC and NVMe should mount.
raspiBackup requires the restore device partitions not to be mounted. Now umount the NVMe partitions (e.g. /dev/nvme0n1p1 and /dev/nvme0n1p2) and use the NVMe device (e.g. /dev/nvme0n1) as parameter for restore option -d.