ROMFS. How it used? Is SD card needed?

Hello. I need help in understanding of some details for ROMFS
As i understood, ROMFS is used for airframe config-files. It uses microSD (mounting function in rcS script)

I have any questions
1.Is it means (microSD using) that I cannot save (or write) any information to SD card during firmware works (ROMFS described as ‘read-only’)?? I planned to save any log (prefer in FAT32 format), but… is I can write anything with ROMFS and how?
2. Can we use internal (or other flash, not microSD) for ROMFS??
3. What interface used for microSD by default in PX4 (I develop custom board and SD card can do transfers through SPI or native SDIO interface)?
4. Can I get along from ROMFS?


So the ROMFS is a filesystem, so a couple of folders and files, which are baked into the ROM, so the firmware which is flashed to a Pixhawk. This means that these files are never on the SD card but are mounted virtually.