In the bios interface of Serveraid controller is possible to set the PHY speed. Beside this there is a parameter called CRC check which can be set to true or false.

Knowing this, some questions:

1. What CRC does exactly? Accordingly to wikipedia it should be an integrity check but how does it work?
2. I discovered that setting this parameter to false my disks are finally recognized as sata2 rather than sata1 and speed are really increased. Why?
3. I found [this](ftp://ftp.software.ibm.com/systems/support/system_x_pdf/ibm_sw_srsupp_9.00_anyos_sraid.pdf) IBM paper in which they say: 'CRC Checking—(Default: No) Determines whether the controller verifies the
accuracy of data transfer on the Serial bus. CRC Checking should be disabled on the
controller and all devices if any device supported by the controller does not support
CRC Checking." How do I discover if a hdd supports CRC?
4. If CRC is disabled and a breaking event occurs, is there a risk?