FAQ
Hi Arun,

Consider setting dfs.balance.bandwidthPerSec to something as high
as 20971520 for the balancer and the setrep. You can do this by supplying
-D at the command line.

Your strategy for getting data onto the 5 nodes is correct: balance and
setrep. Just understand these things take time.

Hope this helps.

Alex
On Wed, Jul 7, 2010 at 4:09 PM, Arun Ramakrishnan wrote:

Hi guys.

I have more than a specific question. I am going to layout the steps I
have taken. Please comment on what I can do better.



I was trying to to add 5 nodes to my existing 10 node cluster and also
increase the replication factor from 2 to 3.

I thought I don’t have to run the balancer cause it would most likely put
the new replicas into the new nodes.



There are about 500k blocks.

I wanted to get it all stabilized(replication and balancing) within 24
hours. Its more than 24 hours now and fsck reports 30% under replication. Is
there a way to force hdfs to use balance/replicate more aggressively.



It would be great if someone explained what/when things happen to blocks in
the context of

1) Rebalancing

2) –setrep

3) Restarting cluster with a higher/lower replication factor.



A few questions and a few issues here.

1) When you restart the cluster with a higher than previous
replication value. Does it also apply to existing blocks or only to new
blocks being created ?

2) Does the balancer take into account under replication of blocks or
does it blindly start moving existing blocks to reach threshold ?





A very specific problem . I am having this strange problem where the
–setrep hangs on one particular block for hours. Is this because its corrupt
?. But, fsck said its healthy.





Thanks

Arun

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