I have several disk-less clusters. They work very well for multiple test environments. I have a bunch of older boxen with only 100Mbit eNet and the file server

I have several disk-less clusters. They work very well for multiple test environments. I have a bunch of older boxen with only 100Mbit eNet and the file servers use gigE. My configuration uses bootp & PxE. For even better performance you may want to look at iSCSI, FCoE or ATA over Ethernet (AoE) I prefer the later two as they run at Layer 2 not 3 and thus are better for data center deployment. It's not just the cost saving on disks. You get reduced power consumption and less noise. You could also look at using CompactFlash cards with a CF-to-IDE adaptor, it's excellent for read-mostly system disk.