Using irm to add disk

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Hello, I'm adding additional disk to a storage works 2300 attached to a RAID 4si PCI controller. I've never used the irm utility before, and would like some reassurance. The new disk is 4 74gb where the existing is 36gb, so I need to add a new logical drive (raid 5). I don't want to mess up the existing configuration, and wonder if I should use the automatic configuration, or view/add. In the manual it states that using automatic will NOT affect pre-existing drives, but a coworker here states that this may not be true. Anyone here used the automatic configuration before, or should I add manually? Thanks, Ed