On Fri, 2012-02-10 at 00:45 -0800, Dan Williams wrote:

It is possible for a host to get "locked out" from talking to sata
devices in the domain if, for example, its sas address changes but the
expander topology has existing affiliations with the old address.  If
the system is booted userspace can write to
/sys/class/sas_phy/<phy-X>/hard_reset to clear the affiliation, however
if this condition exists for the root device the module parameter can be
used to promote all ata resets to hard resets.

I don't quite understand this.  Are you saying we can't (or shouldn't)
execute 

/sys/class/sas_phy/<phy-X>/hard_reset

on the root device for some reason?

After the system is booted this state can be cleared via
/sys/module/libsas/parameters/force_hard_reset

I really don't think a module parameter for this is such a good idea ...
it effectively promotes all soft resets to being hard ones, which can
have a lot of unintended consequences.

James