Re: Accessing the same disk via multiple channels

[Bernd Eckenfels <ecki@calista.eckenfels.6bone.ka-ip.net>]

In article <20030213194917.GA8479@quadpro.stupendous.org> you wrote:
> Each server is equipped with 2 FibreChannel cards. The SAN is
> configured to present the same disk (which is in fact a virtual
> Symmetrix device) over two channels. This means the host sees
> two physical devices (as far as that host's concerned) which is
> in fact really only one device. In linux terms: /dev/sda and /dev/sdc
> are exactly the same disks, but the (standard) OS doesn't know this.
...
> How does linux as it is now handle the situation of one physical device
> presented via multiple paths (without extra software)?

You can use the multipath option to md which can do that.

Basically there are two options, a failover and a load balancing option. The
problem with failover is, to detect the actual failure reliable, toe problem
with load balancing is, that not all san configurations allow this.

http://www-124.ibm.com/storageio/multipath/md-multipath/index.php

this is at least in 2.4.20-xfs

Greetings
Bernd
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