Archive doesn't work for me.

I'm trying to archive my Informix system and I can't get it to work. My system is on a IBM RS-6000 320 and the tape is on a IBM RS-6000 540. My tape parameters are block size = 4K and tape size = 2300000K. When I try to archive on the tape I get an invalid argument and what I've found out is that the tape wants to get the parameter 'conv=sync' also. My dbspaces are in three cooked files of 5000, 41250 and 42500 pages each, and the pages are 4K so my dbspaces are multiples of the tapes block size (0.5K) so there should be no need to sync the files. If I try to archive to a file on a disk on the same remote machine then there is no problem. I tried to solve the problem by catching the 'rsh' command from informix and feeding it the 'conv=sync' parameter and then I could successfully archive on the tape BUT when I tried to restore it again I got an error reading the system control information. Is there anyone who can tell me whats going on and why and how it can be solved? Gaukur. (PS. I backed up the cooked file containing the root dbspace of 20480000bytes with the command 'cat [file] | rsh [rem-machine] dd of=/dev/rmt0.1 bs=4096' on the tape and then restored it with 'rsh [rem-machine] dd if=/dev/rmt0.1 bs=4096 > [file]' and got a file of 20979712bytes but informix didn't seem to mind about the size difference and I could access my database?!?!?!) Thanks in advance.