i have motherboard gigabyte H61M-s1 (which is sata 2.0) and i'm planning to buy hard disk WD5000AAKX (which is sata 3.0) is this HDD is compatible with this motherboard and which sata cable is required for 2.0 or 3.0 !
In general, I agree there SHOULD be no issue however:
I had an issue and did some research and it was recommended to replace my SATA2 cable with an official SATA3 one. A LOT of people say it makes no difference but since my SATA2 cable worked fine with other drives, and using an official SATA3 cable solved my issue I can't agree with that.
Having said that, many people don't have any issues with SATA2 cables on SATA3 hard drives. So go ahead and use it, then run a drive diagnostic to see if any errors occur.