Hi,
> Do you have more than one device mounted and if so are you sure you are working
> on the right one?
As often, the problem turned out to be a simple one.
With OpenWRT, /var is just a symlink to /tmp - which itself is located
on a ramdisk.
After moving the data-directory to /postgresql, everything worked as
expected (however made auto-vacuum less agressive to reduce writes to
the usb flash drive).
So I have now a perfectly fine working postgresql instance running on
a 35$ wlan router :)
Thanks for working on this great piece of software, Clemens