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HDFS >> mail # user >> Accessing list of blocks on a datanode via Java interface


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Yaron Gonen 2012-07-06, 14:28
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Harsh J 2012-07-06, 14:58
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Re: Accessing list of blocks on a datanode via Java interface
Thanks for the fast reply.
My top goal is to backup any new blocks on the DN.
What i'd like to do is to go over all the blocks in the DN and to make a
signature for any one of them. I'll compare that signature with a backup
server.
I guess another feature will be to check only new blocks, so i'll have to
look at the metadata of each block.
On Jul 6, 2012 5:59 PM, "Harsh J" <[EMAIL PROTECTED]> wrote:

> When you say 'scan blocks on that datanode', what do you mean to do by
> 'scan'? If you want merely a list of blocks per DN at a given time,
> there are ways to get that. However, if you want to then perform
> operations on each of these block remotely, then thats not possible to
> do.
>
> In any case, you can run whatever program you wish to agnostically on
> any DN by running it on the dfs.datanode.data.dir directories of the
> DN (take it from its config), and visiting all files with the format
> ^blk_<ID number>$.
>
> We can help you better if you tell us what exactly are you attempting
> to do, for which you need a list of all the blocks per DN.
>
> On Fri, Jul 6, 2012 at 7:58 PM, Yaron Gonen <[EMAIL PROTECTED]> wrote:
> > Hi,
> > I'm trying to write an agent that will run on a datanode and will scan
> > blocks on a that datanode.
> > The logical thing to do is to look in the DataBlockScanner code, which
> lists
> > all the blocks on a node, which is what I did.
> > The problem is that the DataBlockScanner object is instantiated during
> the
> > start-up of a DataNode, so a lot of objects needed (like FSDataSet) are
> > already instantiated.
> > Then, I tried with DataNode.getDataNode(), but it returned null
> (needless to
> > say that the node is up-and-running).
> > I'd be grateful if you can refer me to the right object or to a a guide.
> >
> > I'm new in hdfs, so I'm sorry if its a trivial question.
> >
> > Thanks,
> > Yaron
>
>
>
> --
> Harsh J
>
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Harsh J 2012-07-06, 18:06
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Yaron Gonen 2012-07-06, 18:58
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Harsh J 2012-07-07, 01:50
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Yaron Gonen 2012-07-07, 09:17