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[Linux-cluster] Failover w/GFS and IBM FAStT600



I setup GFS 6.0.0-15 on two IBM xSeries 345 servers running RedHat AS 3.0 server.  The plan is to add a third server in the near future.
 
Each server has two QLogic 2312 HBAs (A and B) and are connected to two IBM SAN switches (A and B).  The A HBA on each server is connected to the A SAN switch and the B HBA on each server is connected to the B SAN switch.  The switches are not connected to each other.
 
Through the SAN switches the servers connect to a IBM FAStT600 (non-turbo) storage server.  The A controller on the FAStT600 connects to the A SAN switch and the B controller on the FAStT600 connects to the B SAN switch.
 
There are three LUNs on the FAStT600.  LUNs 0 and 2 prefer the A controller on the FAStT600 and LUN 1 prefers the B controller on the FAStT600.
 
I have loaded the QLogic 7.01.01 failover driver for the HBAs on each server.
 
Everything works great normally, but if one of the HBAs loses it's connection to the SAN (I unplug the fiber connection for testing), I start seeing ping-ponging between the A and B controllers on the FAStT600.  The ping-ponging kills performance of the storage server.
 
For example, if I unplug the fiber connection on the B HBA on one of the servers, one server is still accessing LUN 1 through the preferred path on the B HBA and the B controller on the FAStT600, but the server where the fiber was removed from the B HBA is now accessing this LUN through its A HBA and the A controller on the FAStT600. 
 
When the FAStT600 sees I/O for LUN 1 from one of the servers on its A controller it starts using the A controller for LUN 1.  Then, when the FAStT600 sees I/O for LUNA 1 from the other server on its B controller it starts using the B controller for LUN 1.  This results in the ping-ponging.
 
I have been told that RDAC will solve this problem, but this isn't currently an option for my configuration because I do not have the turbo version of the FAStT600.
 
Before I spend the considerable amount of money IBM wants for the turbo upgrade I would like to know if anyone has gotten failover to work properly in a similar configuration to what I have using a IBM FAStT600 without the turbo option.
 
Thank you in advance for your help.
 
--Vincent
 

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