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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6686) Archival Storage: Use fallback storage types
Date Wed, 23 Jul 2014 06:50:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14071430#comment-14071430
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Tsz Wo Nicholas Sze commented on HDFS-6686:
-------------------------------------------

Vinay,
# Good catch.  We should pass excludedNodes.
# For getAdditionalDatanode(), since the write is already started, there are already some
data in the block.  So using replication fallback is correct.  Creation fallback usually is
a subset of replication fallback since if there are not enough storages available, we may
fails creation.  However, if we fail replication, it may result in data loss.

Arpit,
# Good catch.  We need to pass newBlock as a parameter.
# numOfResults indeed is the number of existing replicas (numOfResults is used to determine
whether local host/local rack/remote rack should be chosen from).  numOfReplicas (call it
n) is the number of replicas to be chosen.  In our case, we try to select n storage types
but we may only able to get m < n, where m = storageTypes.size().  So we should update
numOfReplicas.

Thanks both of you for the careful reviews!

> Archival Storage: Use fallback storage types
> --------------------------------------------
>
>                 Key: HDFS-6686
>                 URL: https://issues.apache.org/jira/browse/HDFS-6686
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>         Attachments: h6686_20140721.patch, h6686_20140721c.patch
>
>
> HDFS-6671 changes replication monitor to use block storage policy for replication.  It
should also use the fallback storage types when a particular type of storage is full.



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