I'm relieved to read that most of us have difficulties to understand what is going on, on the onions memory (Memory Technology Device; MTD)*.
OpenWRT is a router OS. So most of routers do not have a hard drive (block device)* in sens of a computer who stores data for ever.
The firmware is a file where gets extracted in a ROM (Read only memory) = /dev/root mounted as /rom.
Now in several layers** the omega-os (openWRT based) prepares the data to use ... How this could look like, I tried to explain already here on a simplified way (see also link to openWRT wiki
[RESOLVED] UNDOO >> USB-Storage-as-Rootfs !!
*What are the differences between flash devices and block drives?
**If we have a look to the partitions now, we also can recognize what is used and produced in witch layer:
root@Omega-24CF:/# fdisk -l
Disk /dev/mtdblock0: 0 MB, 131072 bytes
Disk /dev/mtdblock1: 1 MB, 1150464 bytes
Disk /dev/mtdblock2: 15 MB, 15429632 bytes
Disk /dev/mtdblock3: 7 MB, 7929856 bytes
Disk /dev/mtdblock4: 0 MB, 65536 bytes
Disk /dev/mtdblock5: 16 MB, 16580608 bytes
For me everything is a bit learning by doing now. So I think to put this info's in to the wiki could help several persons. But before i do so, please correct if i see something wrong or to simplified