We didn’t run performance benchmarks on the three boards since the primary purpose of this review is to evaluate possible PCI Express bottlenecks when high-speed controllers, such as SATA 3.0 solutions, are used. Therefore we created a CrossFire setup using two Sapphire Radeon HD 5850 cards. This was more than enough to saturate the PCI Express 2.0 links and show which boards would take a hit on storage performance due to the lack of available bandwidth.
As expected, SATA performance using Marvell's SATA 3.0 controller dives when both x16 PCI Express slots are used in a CrossFire setup on Gigabyte’s P55A-UD6. The two other solutions utilize the PLX chip to dynamically allocate PCI Express 2.0 bandwidth, and don't take as significant of a performance hit.
The results are similar when running a mechanical hard drive. The Barracuda XT sports a SATA 6Gb/s interface, true. But it only delivers peak throughput when reading from or writing into the drive’s cache memory. The rest of the time, it's limited to more modest performance specifications. Only the solutions that use the PLX PCI Express switch are capable of delivering high bandwidth.