[jira] [Updated] (HDFS-7928) Scanning blocks from disk during rolling upgrade startup takes a lot of time if disks are busy

["Rushabh S Shah (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-7928?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rushabh S Shah updated HDFS-7928:
---------------------------------
    Attachment: HDFS-7928.patch

Attaching a patch.

> Scanning blocks from disk during rolling upgrade startup takes a lot of time if disks are busy
> ----------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7928
>                 URL: https://issues.apache.org/jira/browse/HDFS-7928
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: Rushabh S Shah
>            Assignee: Rushabh S Shah
>         Attachments: HDFS-7928.patch
>
>
> We observed this issue in rolling upgrade to 2.6.x on one of our cluster.
> One of the disks was very busy and it took long time to scan that disk compared to other disks.
> Seeing the sar (System Activity Reporter) data we saw that the particular disk was very busy performing IO operations.
> Requesting for an improvement during datanode rolling upgrade.
> During shutdown, we can persist the whole volume map on the disk and let the datanode read that file and create the volume map during startup  after rolling upgrade.
> This will not require the datanode process to scan all the disk and read the block.
> This will significantly improve the datanode startup time.



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