CDH4 VM : Unable to access DFS, Missing blocks

[#1]

I've got few problems dealing with cloudera CDH4 vm while working on a few PIG scripts.

1. Name node frequently goes into safe mode. Any reasons for this? I bring back to normal but problem persists quite frequently.

2. Says 100% DFS used. How to improve DFS memory? Whats the difference between Heap Memory and Non-Heap Memory in DFS. 

3. Says : WARNING : There are 132 missing blocks. Please check the logs or run fsck in order to identify the missing blocks. 

4.Unable to access DFS , HTTP ERROR 500

[#2]

1. You can find out why the namenode is in safemode with "hdfs dfsadmin -safemode get"

2. I don't understand-- can you be more detailed?  What are you out of, memory or disk space?

3. Is the replication factor greater than the number of datanodes?

4. is the DFS down?

Colin