Thanks a lot. What I now did is updating all packages over the internet. Now the USB-Ports run with approx. 10MB/s in single mode and in a mirror of two devices with about 20MB/s. That's fine so far.
The next problem is, that when I scrub a mirror of two devices I get an I/O-Error. A raidz runs fine. Next time I will do a screenshot and post it in a new thread. Thanks again for your support. Best regards Martin -- This message posted from opensolaris.org