problem installing server raid

[Luca Ferrari]

Hi all,
I'm trying to install ubuntu server with a raid software (multiple devices). 
I defined partitions and associated them, but then I found I made a mistake, 
so I erased all the partitions and did the process again. The problem is that 
now I'm unable to delete a raid device since the system tells me it could be 
in use. I stopped the system, started it again, and then the md are 
disappeared, but as soon as I enter in the md configuration they appear again 
and are locked (I cannot delete them).
I've tried to delete all, redo and write to disk, then reboot, but again the 
md are not shown immediatly but become visibile as soon as I enter in the md 
configuration tool.

How can I delete them and re-define?

Thanks,
Luca