Hi uboot. Thx for the help. I realize my explanation of what i did was not complete and confusing..but you saved my efforts with your help! Thx
First i tried this tutorial, using Minitool to repartition my PRS-T1, but somehow it got corrupted. So, i restored my original image with RoadKill Diskimage and started all over again, but now with this tutorial:
In this tutorial they use Acronis Disk Director Home (ADDH).
One of the first commands in this tutorial is indeed to make a tar from the system partition, but I couldn't restore it in the end.
So, I used rescue_1.04.zip after repartitioning to restore the system and used your command to reformat the data partition (mkfs.ext4 -L data -m 0 -j /dev/mmcblk2p9). But, with this rescue image, i had to choose my language and Region again on every boot, so I used this rescue image instead: sdrescue_1.04_porkupan.7z
Afterwards i used your format command for the data partition again and now everything is fine!
However, you state that your Package 1 "rescue_1.04.zip" creates more inodes, which is handy for rooting the device later. Is it really neccesary to get more inodes?
(Now i've used Package 2 ( sdrescue_1.04_porkupan.7z) which don't make more inodes)
I rooted my PRS-T1 afterward with AMR and Apps2SD and everything is working ok.
Using ADDH for repartitioning is working ok, but you have to reboot your PC after every repartitioning step, so it takes some time, but it does the job really well.
My other problem, that i couldn't see my PRS-t1 drive with Minitool or Acronis Disk Director is solved. I forgot to put the rupor-rescue.7z image on my external SD-card to boot in recovery mode. If you boot in recoverymode with this image on the SD-card, you are able to see your PRS-T1 drive on your pc and make and restore images from it.
So, everything is working ok now, i have lots of extra storage to put my programs on.
Again, thanks for the help!