Quick question
 

How many Disk Lun's can Linux see?

Not sure of the limit myself. I have read you can go from say /dev/hda to /dev/hdz then to /dev/hdaa to /dev/hdzz. Same for /dev/sd** as well for scsi/usb/firwire/*. Drive can be partition using 4 primary partitions. To go beyond one primary must be an extended partition that contains the rest of logical drives. Extaned partition acts as a container for the logical drives.

Misc link on lun size.
http://techpubs.sgi.com/library/tpl/..._html/apb.html

Technically the limit would be somewhere on the order of... a hell of a lot more than you could conceivably hit. Even with clustering it is unlikely you would hit that high. But even assuming just the hda-hdz, that would be 26, add the sda-sdz, we are now at 52. Assuming you wanted hdaa-hdzz and sdaa-sdzz... Yeah... now you are looking at 26^26x2. That is quite an absurdly large number. 6.156*10^36x2 = approximately 12312239160400000000000000000000000000 drives. Even clustering, good luck with that.

editted to fix number of 0s.