Teaching gmultipath about path cost/priority

[Trent Nelson]

Hi again Matt,

    I'm sure I'll eventually find a subsystem relevant to me that you *didn't*
    author, but for now, I have some gmultipath questions.

    Basically, the entire approach is perfect for me.  As all my SAN targets
    are JBODs (i.e. I don't have any targets that could saturate a single HBA
    and thus would benefit from active/active multipathing), active/passive
    is exactly what I want.

    But... in my case, all paths are not equal.  My fabric has four switches 
    and is fully meshed; a host may have up to four HBAs, each one connected 
    to a separate switch.  From a redundancy and failover perspective, I've
    made sure there are an abundance of paths available to a single disk.

    However, unless something has failed, there's only one path I want to use,
    as I've pre-planned that path to be the most optimal.

    It sounds like the order gmultipath uses to select paths is derived from 
    the order it tastes disks -- something I have very little control over.

    It'd be ideal if there was a way of teaching gmultipath about a path
    cost/priority, so that it can make an informed decision about which
    path to choose a) when first initializing, and b) during failover.

    Thoughts?

    Regards,
    
        Trent.