Sata 6.0 Hard disk

You need to buy a SATA 6.0 Gb/s hard drive to see any benefit from the SATA 6.0 Gb/s motherboard (though only a SSD pushes the limits of the controller's bandwidth).

Here would be my recommendation: http://www.newegg.com/Product/Product.aspx?Item=N82E168... other wise stick with a SATA 3.0 Gb/s drive like this: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

On a conventional hard drive, there is no real benefit to 6gb sata vs. 3gb sata, either on the motherboard or the drive. 6gb transfer rates apply only to buffer to sata operations. On a hard drive, the mechanical motion is the only real determinant of speed. Ignore 6gb as an issue.

There is a case for 6gb sata if you are looking at a SSD. Even then, random i/o performance is why we get a SSD. The synthetic sequential benchmarks are largely irrelevant.

To answer your question directly, no - you don't need to buy a SATA 6Gbit/sec hard drive to use with the SATA 6Gbit/sec connectors on your motherboard. SATA is designed to be backward compatible - if you plug a 6Gbit/sec drive into a 3Gbit/sec port then the two of them autonegotiate the fastest speed that both of them are capable of. Every once in a while a particular drive may fail to autonegotiate with a particular motherboard chipset - in that event most SATA drives have a jumper you can set to force them to the slower speed to solve the problem.

In short - don't worry about what kind of drive you buy, as long as it's some version of SATA (and not IDE, for example).

As the others have noted, mechanical hard drives don't get any performance benefit from SATA 6Gbit/sec, so there's no particularly good reason to pay extra for one. But most of the newer drives are moving in that direction since the manufacturers who make SATA chipsets are moving away from making the older, slower chips.

Even an SSD with SATA 6Gbit/sec capability will work when connected 3Gbit/sec motherboard port - but since an SSD has no mechanical delays that might actually slow it down. Best to connect SSDs to the fastest ports you have available.

Does anyone has any idea what is raid, and how it can improve my system ( intel i5 2500k with z68 chipset performance, if i'm not using any SSD?

Google is your friend

Raid stands for redundant array if inexpensive(independent) disks. It is a means to aggregate multiple drives to get redundancy, or better sequential performance.
It has no real benefit in actual desktop performance; only sequential benchmarks look good, but are irrelevant.

With the Z68 chipset, however, there is a special variant that might be beneficial. It allows a small SSD, or a portion of it(up to 60gb) to be used as a cache in conjunction with a conventional hard drive. Frequently used data blocks will be kept on the ssd, which will speed up I/o to those blocks. It will result in performance improvement that is much better than a hard drive, but not as good as a dedicated SSD.

Best answer selected by developeraslam.