Some things which helped us include setting your vm.swappiness to 0 and
mounting your disks with noatime,nodiratime options.
Also make sure your disks aren't setup with RAID (JBOD is recommended)
You might want to run terasort as you tweak your environment. It's very
helpful when checking if a change helped (or hurt) your cluster.
Hope that helps a bit.
On 05/30/2011 06:27 AM, Gyuribácsi wrote:
Hi,
I have a 10 node cluster (IBM blade servers, 48GB RAM, 2x500GB Disk, 16 HT
cores).
I've uploaded 10 files to HDFS. Each file is 10GB. I used the streaming jar
with 'wc -l' as mapper and 'cat' as reducer.
I use 64MB block size and the default replication (3).
The wc on the 100 GB took about 220 seconds which translates to about 3.5
Gbit/sec processing speed. One disk can do sequential read with 1Gbit/sec so
i would expect someting around 20 GBit/sec (minus some overhead), and I'm
getting only 3.5.
Is my expectaion valid?
I checked the jobtracked and it seems all nodes are working, each reading
the right blocks. I have not played with the number of mapper and reducers
yet. It seems the number of mappers is the same as the number of blocks and
the number of reducers is 20 (there are 20 disks). This looks ok for me.
We also did an experiment with TestDFSIO with similar results. Aggregated
read io speed is around 3.5Gbit/sec. It is just too far from my
expectation:(
Please help!
Thank you,
Gyorgy
