hadoop becomes very slow in Eucalyptus VMs

[Shi Yu]

I installed hadoop-0.20.2 in Eucalyptus VM environment. The file system 
is based on glusterfs, so it is a shared NAS.  Though the nodes are much 
powerful (8 cores + 15G memory), I found the response of hadoop namenode 
and data nodes became very slow. For example, after running 
start-all.sh,  the datanodes take more than 5 minutes to be ready.  The 
safe mode time is really really long.  Moreover, the program also runs 
much slower than it did on old physical cluster nodes.  I have tried 
running hadoop on a cluster containing 15 VM nodes, also on a pesudo 
cluster on a single VM, all very slow.  Is it because NAS is an IO 
bottleneck?  The HDFS is created on top of glusterfs like reinventing 
the wheel, so I tried to adjust the replication setting to different 
values (1 to 4) but no improvement.  I haven't tried CDH3 package yet. I 
wonder whether switching to CDH3 would bring any significant 
improvement.   Any suggestion about this issue is highly appreciated.

Shi