Let's get the terminology right...
You don't create a LUN, you create a virtual disk. The virtual disk is then mapped to the SCSI LUN address space of each defined host when you 'present' it. You normally have 4 paths, so there are 4 different SCSI LUNs to access a single virtual disk.
It is important to understand that on every EVA (3000/4000/5000/6000/8000) a single virtual disk is managed by one of the controllers at a time - a different virtual disk, of course, can be managed by the other controller.
On the new EVAs (4000/6000/8000) you can do I/O through the non-managing controller as well, but there is a performance loss, because the data need to be re-routed over the mirror ports to the managing controller. It is not a great deal for write I/Os, because the data is usually sent anyway to go into the mirror cache, but the read I/Os will create additional traffic.
The paths through the managing controller are called the performance paths and I recommend that you only use them. That will give you two paths with 200 MegaBytes/second - should be OK, because the EVA4000 has two back-end loops with 200 MegaBytes/second anyway.
In most cases you are dealing with multiple virtual disks. You should divide them over both controllers so that you have some kind of load sharing and can make efficient use of all 4 paths.
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