Thank you for your answer, but it didn’t solve the Problem.
Latest firmware was installed and there was no firewall aktivated.
I tested it from several PC and devices in different locations. During the testing i noticed something, that might specity the problem.
For testing i copied a folder with pictures and a larger file (50MB). While copying the “Picturefolder” there was no change or improvement in copying-speed.
When i transfered the larger file it was uploaded with up to 150kb/s, so it took just a few secondes to copy the larger file on my N900 drive. After transfering the file the copying process more or less stoped and it took another minute to complete the whole process.
So in my point of view the problem is not the upload/download rate, it seems that there are some “handling” problems with the files. And again i don’t know what to do…