Thanks for your answer, but I'm not sure to understand...
1/ I need a harware interface to connect the ST external HD plug (ACSI) to my HD (SCSI), right? And there are some different products to do that, but where can I find them online?
2/ I need a driver such as the one from Atari. I have found it and downloaded from the web.
3/ this I don't understand... what's missing after 1/ and 2/