raidreconf "disk too small"

Hello List

Experimenting with Software-Raid 5, I tried to expand an array with 3 partions.
I wanted to add one more partittion with raidreconf.
I took the /etc/raidtab, copied it and made a newraidtab, as subcribed in the Howto.
But when I ran raidreconf --test -o ... -n .. -m /dev/md0, I get the message
/dev/hdx too small (0kB).
I wrote hdx, because it seems that it is the first partition in mentioned in the
raidtabfiles .
I changed the configuration with different disks and different partitons.
Every time the messages prints out the first partition in raidtab.
The partitions are 9.3GB.
The disks I tried are 3X 120 GB mator, 1X 20GB IBM and 1X 20 GB IBM.

Any idea?
Thanks

Peter