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https://issues.apache.org/jira/browse/HDFS-11190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15974089#comment-15974089
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Virajith Jalaparti commented on HDFS-11190:
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Thanks for the comments [~ehiggs].
bq. Why {{PROVIDED}}, {{DISK}} and not {{DISK}}, {{PROVIDED}}?
This is because when {{PROVIDED}} blocks have a replication 1, we want them to
be stored on {{PROVIDED}} storage and not on {{DISK}}. When we increase the
replications, the preference is {{DISK}}.
The idea behind {{moveProvidedToEnd}} was that if we have multiple locations
for a {{PROVIDED}} block, then we would like clients to prefer local replicas
(on {{DISK}} or others) rather than the {{PROVIDED}} storage. So, we order the
locations with the {{PROVIDED}} storages at the end.
Yes, using {{Arrays.sort()}} would have been much simpler. I will replace the
current implementation with one using {{Arrays.sort()}}.
> [READ] Namenode support for data stored in external stores.
> -----------------------------------------------------------
>
> Key: HDFS-11190
> URL: https://issues.apache.org/jira/browse/HDFS-11190
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Virajith Jalaparti
> Attachments: HDFS-11190-HDFS-9806.001.patch,
> HDFS-11190-HDFS-9806.002.patch, HDFS-11190-HDFS-9806.003.patch
>
>
> The goal of this JIRA is to enable the Namenode to know about blocks that are
> in {{PROVIDED}} stores and are not necessarily stored on any Datanodes.
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