GEOM for multipath? How?

Danny Howard dannyman at
Wed Nov 9 21:25:35 GMT 2005


Alas, my fancy Engenio dual-FC disk array is inaccessible to me for
testing. :(  But we are working on switching over to RHEL due to
availability of FC multi-path redundancy drivers for RHEL but nada for

I was reading Linux' md man page, which sounds awfully similar to geom,
and they have a provider called:

       MULTIPATH is not really a RAID at all as there is only one real device
       in a MULTIPATH md array.  However there  are  multiple  access points
       (paths)  to  this  device, and one of these paths might fail, so there
       are some similarities.

       A MULTIPATH array  is  composed  of  a  number  of  logical different
       devices,  often  fibre channel interfaces, that all refer the the same
       real device. If one of these interfaces fails (e.g. due to cable prob-
       lems), the multipath driver to attempt to redirect requests to another

And I says to myself "AHA!  Multipath should be easy to implement on
FreeBSD as well, via geom."  But I can't find an obvious way given
existing geom utils to do this.  And like I said, the box I'd use this
on is inaccesible for now.

Basically, I'd want a provider, that would see two disks, and if it
could talk to one disk, it would, else it would talk to the other.

Anyone here have a multipath capable hardware infrastructure who could
test out some applicable geom config?  Like I say a third time ... I
have a nice Engenio 2882 FC sitting in a Datacenter, 3,000 miles away,
that is connected to a system that is offline.  I get to visit after
Thanksgiving ... :/



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