Although Debian runs entirely off the internal microdrive/ compact flash, the NAND flash area is still accessible.
It has two nodes: /dev/mtdblock2 and /dev/mtdblock3
The question is to mount them we have to specify the filesystem type. What is it?
I tried -t auto and -t jffs2 but no luck. ("mount: you must specify the filesystem type")
Now I think of one good use of the NAND flash area: to put backups of useful scripts, config files, etc in this "safe" area. It will survive reflashing of kernel and even reinstallation of the whole system!