i have an OWC data doubler with a 500 GB HD in the optical drive sata port and an SSD in the main HD sata port. the system stopped recognizing my boot SSD plugged into the HD sata port. If i booted from a recovery disk the only drive i could see was the one connected to the optical drive sata port.
I swapped the SSD to the optical sata port and the 500 GB HD to the main HD sata port. the system would now boot but would not recognize my 500 GB HD. i tried cleaning and reseating cables several times and no matter what i could not get the system to see any drive plugged into that main HD sata port.
i swapped the HD sata cable in hopes that the problem was not a bad sata port on the logic board and lucky for me it worked. i have both drives available and everything has been working with no issue for about a week now. start to finish took probably 15-20 minutes tops, but keep in mind that i've already been tinkering with the internals and know my way around pretty well by now.
this replacement is stupid easy, i checked the guide beforehand and never had to check it during the process. that said, i still think the guide on this site is useful for anyone attempting the swap who many not be the most confident. at the very least, being able to check the guide before you attempt the swap lets you know what you're getting into.