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From Colin McCabe <cmcc...@alumni.cmu.edu>
Subject Re: Is there a way to get a Block through block id?
Date Mon, 20 Jan 2014 19:46:37 GMT
In order to uniquely identify a block in hadoop 2.2, you are going to need
both a block and a block pool ID.  You can construct a Block object with
those two items.

On Wed, Jan 15, 2014 at 8:46 AM, Yu Li <carp84@gmail.com> wrote:

> Dear all,
> As titled, I actually have two questions here:
> 1. In current releases like hadoop-2.2.0, is block id unique and able to
> locate a Block in HDFS? I'm asking because I could see HDFS-4645 is trying
> to resolve the uniqueness issue. However, from the code comment it seems
> block id is expected to be unique
It's expected to be unique within a block pool.  You can get the block pool
ID you are using from your FSNamesystem object in 2.2.


2. It seems there's no method to get a Block object through a block id.
> However, there's some scenarios need such method, like if I use the
> FavouredNode feature to create logical datanode group and planned to put
> some data within a group, then I might need to periodically check whether
> there's block somehow placed outside the group, and move it back. In such
> scenario, I would need to first get block ids, then move. But to move them,
> it seems we need a Block instance to initiate the ExtendedBlock object.
> Any suggestion, or reference to existing JIRA would be highly appreciated,
> and thanks in advance!
> --
> Best Regards,
> Li Yu

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