@cas You wrote:
Is there supposed to be some level of compression built in there?
Yes, I think so.
See also in OpenWrt's Filesystems
About my second 'Trial and Error' example
The size: 512.0K - That's ok
The used: 196.0K - That's not empty
So something looks off with that partition.
Unfortunately I don't know the jffs2 filesystem too well. (Frankly speaking I don't know it at all ;-)
I guess the "used 196.0K" on this "empty" mtd7 can be some kind of 'system administration area' - eg. for journalling and so.
Please look at the 'Used / Available' figures during the whole process.
It's quite funny interesting - isn't it?
BTW I'm only interested on wear leweling now.