hadoop-common-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Stijn De Weirdt <stijn.dewei...@ugent.be>
Subject data distribution in HDFS
Date Mon, 02 Apr 2012 16:54:24 GMT
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 

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,


View raw message