Bugzilla 577967 added code for powering down ahci DMA engines if there's no device attached. This appears to occasionally result in a failure to identify devices and a consequent failure to boot.
Created attachment 421812 [details]
Patch to fix this
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release. This request is not yet committed for
Posted on June 9th.
Patch(es) available on kernel-2.6.32-42.el6
We've booted numerous snapshots since Beta on AHCI systems. Additionally setting of link power has not affected subsequent boots or devices already attached on any of the systems I've tested AHCI link power management on.
Hotplugged devices are the exception where link power management has to be set to max_performance in order for device detection to work. The kernel should disallow this on any hotpluggable SATA port already.
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.