Your description sounds vague, to me .. "Slave stanby saver" , huh ?
Based on what you have said, so far, I can only suggest that you try hooking your boot/system drive to (in turn) the primary storage controller .. or (2) any main secondary controller..
... If you have more than one controller, you will very likely have two different colors of SATA headers/ports. I'm just saying ... "try any/both controllers" and be sure that the boot device is "seen" and properly sensed and saved (as primary boot device), in setup/bios.
I must admit, tho, ... I really have no clear understanding of your config (hw or sw) ... so, unless one of us becomes a major psychic ... or unless we get a very much clearer picture of your config AND your "problem" ... There is really no way we can be of much (if any) assistance.
... I think this (lack of clear and pertinent info from you) may be why so few techs have pitched in to help us with this thread ... but, believe me, ... you don't want a bunch of techs just blurting out bunches of "suggestions" when they cannot even understand the problem clearly (if at all) ..
= Alvin =