hi all,
i'm just started to play around with hdfs+mapred. i'm currently playing
with teragen/sort/validate to see if i understand all.
the test setup involves 5 nodes that all are tasktracker and datanode
(and one node that is also jobtracker and namenode on top of that. (this
one node is running both the namenode hadoop process as the datanode
process)
when i do the in teragen run, the data is not distributed equally over
all nodes. the node that is also namenode, get's a bigger portion of all
the data. (as seen by df on the nodes and by using dsfadmin -report)
i also get this distribution when i ran the TestDFSIO write test (50
files of 1GB)
i use basic command line teragen $((100*1000*1000))
/benchmarks/teragen, so i expect 100M*0.1kb = 10GB of data. (if i add
the volumes in use by hdfs, it's actually quite a bit more.)
4 data nodes are using 4.2-4.8GB, and the data+namenode has 9.4GB in
use. so this one datanode is seen as 2 nodes.
when i do ls on the filesystem, i see that teragen created 250MB files,
the current hdfs blocksize is 64MB.
is there a reason why one datanode is preferred over the others.
it is annoying since the terasort output behaves the same, and i can't
use the full hdfs space for testing that way. also, since more IO comes
to this one node, the performance isn't really balanced.
many thanks,
stijn
