Date: Thu, 10 May 2012 08:13:29 -0700 From: Trent Nelson <trent@snakebite.org> To: "mj@feral.com" <mj@feral.com> Cc: "freebsd-geom@freebsd.org" <freebsd-geom@freebsd.org> Subject: Teaching gmultipath about path cost/priority Message-ID: <4A6AB54F-A0B3-40A6-A8E4-EE9992B5C52D@snakebite.org>
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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 target=
s
are JBODs (i.e. I don't have any targets that could saturate a single H=
BA
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 switche=
s=20
and is fully meshed; a host may have up to four HBAs, each one connecte=
d=20
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 u=
se,
as I've pre-planned that path to be the most optimal.
It sounds like the order gmultipath uses to select paths is derived fro=
m=20
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,
=20
Trent.=
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