Spin Down/Hibernate SATA harddisk

[herbert langhans <w3%langhans.com.pl@localhost>]

Hi List,
a question about SATA disks under NetBSD.

If you have two SATA HDs connected and you have to use only SATA1 - is
there an option to spin down or hibernate SATA2?

SATA1 is always in use (for server), SATA2 can be unmounted (archive or
backup, rarely required). 

Is there some command/utility/method to stop SATA2 spinning? Or may it
stop when umounted (hardware of harddisk)? Any experience or ideas about
it?

Thanks!
herb langhans