When launching the Intel Matrix Storage Console and reviewing the disposition of a mirrored pair of Seagate SATA 3.0Gb/s drives, I noted the Serial ATA transfer mode reported as Generation 1.
SATA host adapters typically support autonegotiation, however, with the Intel ICH10R this does not seem to be the case with RAID enabled. Note: It does work with standard AHCI mode on this chipset.
Seagate drives ship with a jumper enabled for 1.5GB/s mode. One must remove this jumper to force the drive in 3.0GB/s mode.
Reference: Seagate ST3500320AS product manual