Intel just announced that it has identified a bug in the 6-series chipset, specifically in its SATA controller. Intel states that "In some cases, the Serial-ATA (SATA) ports within the chipsets may degrade over time, potentially impacting the performance or functionality of SATA-linked devices such as hard disk drives and DVD-drives.".
The Failure Manifested
I asked Intel how we’d know if we had a failure on our hands. The symptoms are pretty simple to check for. Intel says you’d see an increase in bit error rates on a SATA link over time. Transfers will retry if there is an error but eventually, if the error rate is high enough, you’ll see reduced performance as the controller spends more time retrying than it does sending actual data.
Ultimately you could see a full disconnect - your SATA drive(s) would not longer be visible at POST or you’d see a drive letter disappear in Windows.
It’s Limited to 3Gbps Ports Only
Interestingly enough the problem doesn’t affect ports 0 & 1 on the 6-series chipset. Remember that Intel has two 6Gbps ports and four 3Gbps ports on P67/H67, only the latter four are impacted by this problem.
https://www.anandtech.com/show/4142/intel-discovers-bug-in-6series-chipset-begins-recall