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https://issues.apache.org/jira/browse/HDFS-5442?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13850273#comment-13850273
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LiuLei commented on HDFS-5442:
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Hi Liang Xie,
We can asynchronously do that.
1.  Active NameNode choose three datanodes form first datacenter, the client 
create pipelien with the three datanodes and write data. 
2. When the block is completed, Active NameNode receive the blockReport form 
one datanode, the Active NameNode  judge the block  is needed replication, and 
Active NameNode replicate block to second datacenter.

> Zero loss HDFS data replication for multiple datacenters
> --------------------------------------------------------
>
>                 Key: HDFS-5442
>                 URL: https://issues.apache.org/jira/browse/HDFS-5442
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Avik Dey
>         Attachments: Disaster Recovery Solution for Hadoop.pdf
>
>
> Hadoop is architected to operate efficiently at scale for normal hardware 
> failures within a datacenter. Hadoop is not designed today to handle 
> datacenter failures. Although HDFS is not designed for nor deployed in 
> configurations spanning multiple datacenters, replicating data from one 
> location to another is common practice for disaster recovery and global 
> service availability. There are current solutions available for batch 
> replication using data copy/export tools. However, while providing some 
> backup capability for HDFS data, they do not provide the capability to 
> recover all your HDFS data from a datacenter failure and be up and running 
> again with a fully operational Hadoop cluster in another datacenter in a 
> matter of minutes. For disaster recovery from a datacenter failure, we should 
> provide a fully distributed, zero data loss, low latency, high throughput and 
> secure HDFS data replication solution for multiple datacenter setup.
> Design and code for Phase-1 to follow soon.



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