2 HBA cards, SAN and Arbitrated loop

I was going crazy trying to install Linux on our servers and upon reboot they would do absolutely nothing or give me the GRUB limited shell or simply hang and complain about missing partitions. I suspected something wrong with the boot device: a LUN on an EMC DMX-3 Symmetrix SAN. OEL 4U5 boot CD recognizes the Qlogic qle2460 HBAs perfectly. Kudos there! However, for some reason I noticed my LUN set through both paths, despite having disabled on path (aka HBA) in its BIOS. No matter what I did, the installation CD kept recognizing all LUNs over all paths.
Detailed investigation by our EMC guy showed that the Cisco SAN switches were talking FC-AL (Arbitrated loop), for some reason. After shutting down the second port/path on the SAN switch, the installation CD only saw one set of devices and was no longer confused by all the LUNs that seems to be the same (they were!).

Lesson learned: limit your variables during installation and only use one SAN path. Activate the second path during post installation (you need drivers or software anyway). Powerpath in my case.


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