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From Azuryy Yu <azury...@gmail.com>
Subject Re: Why do some blocks refuse to replicate...?
Date Thu, 28 Mar 2013 23:01:24 GMT
which hadoop version you used?

On Mar 29, 2013 5:24 AM, "Felix GV" <felix@mate1inc.com> wrote:
> Yes, I didn't specify how I was testing my changes, but basically, here's
what I did:
> My hdfs-site.xml file was modified to include a reference the a file
containing a list of all datanodes (via dfs.hosts) and a reference to a
file containing decommissioned nodes (via dfs.hosts.exclude). After that, I
just changed these files, not hdfs-site.xml.
> I first added all my old nodes in the dfs.hosts.exclude file, did
hdfs dfsadmin -refreshNodes, and most of the data replicated correctly.
> I then tried removing all old nodes from the dfs.hosts file, did
hdfs dfsadmin -refreshNodes, and I saw that I now had a coupe of corrupt
and missing blocks (60 of them).
> I re-added all the old nodes in the dfs.hosts file, and removed them
gradually, each time doing the refreshNodes or restarting the NN, and I
narrowed it down to three datanodes in particular, which seem to be the
three nodes where all of those 60 blocks are located.
> Is it possible, perhaps, that these three nodes are completely incapable
of replicating what they have (because they're corrupt or something), and
so every block was replicated from other nodes, but the blocks that
happened to be located on these three nodes are... doomed? I can see the
data in those blocks in the NN hdfs browser, so I guess it's not
corrupted... I also tried pinging the new nodes from those old ones and it
works too, so I guess there is no network partition...
> I'm in the process of increasing replication factor above 3, but I don't
know if that's gonna do anything...
> --
> Felix
> On Thu, Mar 28, 2013 at 4:45 PM, MARCOS MEDRADO RUBINELLI <
marcosm@buscapecompany.com> wrote:
>> Felix,
>> After changing hdfs-site.xml, did you run "hadoop dfsadmin
-refreshNodes"? That should have been enough, but you can try increasing
the replication factor of these files, wait for them to be replicated to
the new nodes, then setting it back to its original value.
>> Cheers,
>> Marcos
>> In 28-03-2013 17:00, Felix GV wrote:
>>> Hello,
>>> I've been running a virtualized CDH 4.2 cluster. I now want to migrate
all my data to another (this time physical) set of slaves and then stop
using the virtualized slaves.
>>> I added the new physical slaves in the cluster, and marked all the old
virtualized slaves as decommissioned using the dfs.hosts.exclude setting in
>>> Almost all of the data replicated successfully to the new slaves, but
when I bring down the old slaves, some blocks start showing up as missing
or corrupt (according to the NN UI as well as fsck*). If I restart the old
slaves, then there are no missing blocks reported by fsck.
>>> I've tried shutting down the old slaves two by two, and for some of
them I saw no problem, but then at some point I found two slaves which,
when shut down, resulted in a couple of blocks being under-replicated (1
out of 3 replicas found). For example, fsck would report stuff like this:
>>> /user/hive/warehouse/ads_destinations_hosts/part-m-00012:  Under
Target Replicas is 3 but found 1 replica(s).
>>> The system then stayed in that state apparently forever. It never
actually fixed the fact some blocks were under-replicated. Does that mean
there's something wrong with some of the old datanodes...? Why do they keep
block for themselves (even thought they're decommissioned) instead of
replicating those blocks to the new (non-decommissioned) datanodes?
>>> How do I force replication of under-replicated blocks?
>>> *Actually, the NN UI and fsck report slightly different things. The NN
UI always seems to report 60 under-replicated blocks, whereas fsck only
reports those 60 under-replicated blocks when I shut down some of the old
datanodes... When the old nodes are up, fsck reports 0 under-replicated
blocks... This is very confusing!
>>> Any help would be appreciated! Please don't hesitate to ask if I should
provide some of my logs, settings, or the output of some commands...!
>>> Thanks :) !
>>> --
>>> Felix

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