Some readings related to Omnia, SATA issues: SATA HDD issues
There you find link to “original” NAS sata controler on Amazon as well some alternatives. It is old and long, but some info is still handy.
Plus all the issues users faced so far (including me).
Since i got my OmniaNAS box i was not able to use two drives at same time. Second channel/drive was having i/o error during rw mount or very shortly after. It seems that second channel is broken or power supply is not able to handle two 4TB disks at once. Not mentioning NCQ issues and sata link stuff (some users have to lower the sata link speed to make it working)