Linux multipath IO (MPIO)

Last week I tried to install Oracle Enterprise Linux, aka Unbreakable Linux, on our new PowerEdge 2950 servers. Installation went without a hitch! So that was good news. A look in dmesg showed the two Qlogic QLE2460 HBAs and the on-board Broadcom dual 1 Gb NICs were recognized perfectly. However, SAN people reported no activity or visibilty on the SAN fabric whatsoever.
I started to read up on Linux multipath IO (MPIO) and found some documentation there. I will have to go back to the data center and try these thing onsite, as remote access is not working yet.

The good news is that MPIO is built-in in Linux kernels since early 2.6 (something like 2.6.5) so by now, these things should be standard. LVM2 includes all the necessary device-mapper packages and utils, so everything should be in place. I simply may need to activate the device mapper with dmsetup or multipathd. We'll see...

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