RAID-0 vs. JBOD?

[Colin Evans]

We're building a cluster of 40 machines with 5 drives each, and I'm 
curious what people's experiences have been for using RAID-0 for HDFS 
vs. configuring seperate partitions (JBOD) and having the datanode 
balance between them. 

I took a look at the datanode code, and datanodes appear to write blocks 
using a round-robin algorithm when managing multiple partitions.  In 
theory, the striping on RAID-0 should be more evenly balanced than this, 
but RAID-0 doesn't seem to give a speedup proportionate to the number of 
drives being striped.  Furthermore, our initial tests seem to suggest 
that the JBOD configuration spends less time in wait state than the 
RAID-0 configuration when running disk-bound jobs.

We're still tweaking our own benchmarks, so we don't have any conclusive 
results yet.  Has anyone done this kind of comparison before?