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From Patai Sangbutsarakum <silvianhad...@gmail.com>
Subject Re: balancer and under replication
Date Mon, 07 Jan 2013 22:25:04 GMT
Thanks Harsh, you're the first, as usual.
Currently, there are 291 active nodes spread in 11 racks. We have
rack-awareness enable for a year (work like a champ).

I ran fsck throughout HDFS again and noticed that majority of the
files that have under repl. blocks
are set to have 255 replicas but actually it can have only 202 replica.

the maximum replica i saw was in a file that is set for 255 replica
and it got 217 replica.

another 4-5 files are complaining "Replica placement policy is
violated for blk_-6514473498006714669_245767971. Block should be
additionally replicated on 1 more rack(s)."

I tried to setrep +1, -1 trick. Still NN didn't try to pump the number
of repl. this time.

So, question would be with 291 nodes in 11 racks would that feasible
to have 255 copies while compliance to rack awareness?

Hope this make sense

On Mon, Jan 7, 2013 at 1:16 PM, Harsh J <harsh@cloudera.com> wrote:
> Under normal operation, NN takes care of under-replicated blocks by itself.
> A file with a replication factor set higher than the cluster's nodes
> will also register its blocks as under-replicated. A common config
> mistake here is the mapred.submit.replication, which is a default of
> 10 (useful for 100 nodes but not otherwise), and you can verify via
> fsck if these affected files are all staging directory MR files which
> fall under this category. If so, just lowering their setrep will help.
> If not the above, there's a chance that a rack misconfig may have
> caused a bad state of replication (a violation of policy), which can
> be fixed by the raise and subsequent lowering of the replication
> factor as you state.
> On Tue, Jan 8, 2013 at 2:18 AM, Patai Sangbutsarakum
> <silvianhadoop@gmail.com> wrote:
>> Hello Hadoopers,
>> Currently my production cluster which is running cdh3u4 has shown
>> Number of Under-Replicated Blocks around 1k blocks.
>> Even though we have balancer run every night somehow the number of
>> under replicate is never go down at all.
>> The question is how HDFS handles under-replication blocks.
>> - will namenode takes care when file that has under-replicated blocks
>> is being used ?
>> or
>> - we need to bump up setrep to kind of trigger the number of replication block ?
>> or
>> - ??
>> Thanks
>> -P
> --
> Harsh J

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