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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1912) Datanode should support block replacement
Date Mon, 22 Oct 2007 22:15:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12536856

Raghu Angadi commented on HADOOP-1912:

> 3. For comment 3, your change is not exactly the same as the logic in the current code.
If you'd merge two checks into one, I will change the code to be [...]

I see now. I misread the code. No need to merge the conditions. thanks.

> Datanode should support block replacement
> -----------------------------------------
>                 Key: HADOOP-1912
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1912
>             Project: Hadoop
>          Issue Type: New Feature
>          Components: dfs
>    Affects Versions: 0.14.1
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>         Attachments: replace.patch, replace1.patch, replace2.patch, replace3.patch
> This jira Data Node's support for rebalancing (HADOOP-1652). When a balancer decides
to move a block B from Source S to Destination D. It also chooses a proxy source PS, which
contains a replica of B, to speed up block copy.  The block placement is carried in the following
> 1. A block copy command is sent to datanode PS in the format of  "OP_BLOCK_COPY <block_id_of_B>
<source S> <destination D>". It requests PS to copy B to datanode D.
> 2. PS then transfers block B to datanode D with a block replacement command to D in the
format of "OP_BLOCK_REPLACEMENT <block_id_of_B> <source S> <data_of_B>".

> 3. Datanode D writes the block B to its disk and then sends a name node a blockReceived
RPC informing the namenode that a block B is received and please delete a replica of B from
source S if there is any excessive replica.
> 4. The namenode then adds datanode D to block B's map and removes an exesive replicas
of B in favor of datanode S.
> In addition, each data node has a limited bandwidth for rebalancing. The default value
for the bandwidth is 5MB/s. Throttling is done at both source & destination sides. Each
data node limits maximum number of concurrent data transfers (including both sending and receiving)
for the rebalancing purpose to be 5. In the worst case, each data transfer has a limited bandwidth
of 1MB/s. Each sender & receiver has a Throttler. The primary method of the class is "throttle(
int numOfBytes )". The parameter numOfBytes indicates the total number of bytes that the caller
has sent or received since the last throttle is called. The method calculates the caller's
I/O rate. If the rate is faster than the bandwidth limit, it sleeps to slow down the data
transfer. After it wakes up, it adjusts its bandwidth limit if the number of concurrent data
transfers is changed. 

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