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https://issues.apache.org/jira/browse/HADOOP-3631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12620842#action_12620842
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dhruba borthakur commented on HADOOP-3631:
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My proposal actually needs three disks irrespective of the number of namedirs.
For starters, the fsimage on all the namedirs will use D1, the edits file on
all the namedirs will be on D2 and the edits.new on all namedirs will be on D3.
Also, since edits and edits.new are on different disks, it is never the case
that the Secondary will read/write to the same disk on which the namenode is
currently logging transactions.
> Transfer of image from secondary name node should not interrupt service
> -----------------------------------------------------------------------
>
> Key: HADOOP-3631
> URL: https://issues.apache.org/jira/browse/HADOOP-3631
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.17.0
> Reporter: Robert Chansler
> Priority: Critical
> Fix For: 0.19.0
>
>
> The transfer of the new image prepared by the secondary name node can
> interfere with client services. Clients observe delays in completing RPCs. In
> general, administrative activities should not be observed by the clients. For
> large clusters, administrators are reluctant to run the secondary name node
> leading to excessive edit logs. (Excessive in the sense that if the cluster
> must be restarted, a long time is required to process the log.)
> Maybe the new image does not have to be transfered; it could be fetched when
> needed.
> Maybe the priority of the transfer task can be reduced so that the transfer
> is not observed.
> Maybe a different transfer protocol is more appropriate.
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