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https://issues.apache.org/jira/browse/HDFS-10857?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15504768#comment-15504768
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Kihwal Lee commented on HDFS-10857:
-----------------------------------

The patch partially brings in changes available in branch-2.7 to removing 
volumes easier.

> Rolling upgrade can make data unavailable when the cluster has many failed 
> volumes
> ----------------------------------------------------------------------------------
>
>                 Key: HDFS-10857
>                 URL: https://issues.apache.org/jira/browse/HDFS-10857
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.6.4
>            Reporter: Kihwal Lee
>            Priority: Critical
>         Attachments: HDFS-10857.branch-2.6.patch
>
>
> When the marker file or trash dir is created or removed during the heartbeat 
> response processing, an {{IOException}} is thrown if tried on a failed 
> volume.   This stops processing of the rest of storage directories and any 
> DNA commands that were part of the heartbeat response.
> While this is happening, the block token key update does not happen and all 
> read and write requests start to fail, until the upgrade is finalized and the 
> DN receives a new key. All it takes is one failed volume. If there are three 
> such nodes in the cluster, it is very likely that some blocks cannot be read. 
> The NN has no idea unlike the common missing blocks scenarios, although the 
> effect is the same.



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