question about LUNs and RH

[Ed Wilts]

On Fri, Aug 19, 2005 at 03:20:52PM -0500, Dana Holland wrote:
> Ed Wilts wrote:
> >Are the FastT controllers active/passive or active/active?  How are you
> >doing your multipathing, if at all?
> 
> They're active/active.  We aren't sure what you mean by multipathing.

With redundant controllers, you have 2 muliple paths to the same
physical device.  With active/active controllers, you see both paths at
the same time and the disk is online to both.  Not only do you have the
2 paths to the disk via the 2 controllers, you also have 2 paths via the
dual HBAs so you have *four* paths to the same disk.

Multipathing means that you've got some software that handles the
redundant paths.  This handles the case where one path goes down but you
still need to access the data on the other path. It allows you to
recover from either a failure of the HBA, switch, or controller.

With RHEL 2.1, you don't have a lot of options for multipathing.  My
guess is you must have set up a software raid device using just the
multipath option.  Alternatively, some vendors have their own multipath
implementations - EMC with PowerPath, HP with SecurePath, and even some
HBA drivers handle certain controllers (e.g. qlogic with HP EVA).
I don't know what IBM normally recommends.

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts at ewilts.org
Member #1, Red Hat Community Ambassador Program