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https://issues.apache.org/jira/browse/HDFS-7896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14964385#comment-14964385
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Walter Su commented on HDFS-7896:
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Slow disk is different with failed disk. A slow disk still can be read. It is
slow maybe because of bad sectors or lifespan or other issues. It tend to fail,
but not fail immediately.
Bad sectors usually means damage of the physical body. To avoid more data
damage, this disk should be read-only, and warn user. So it can be replaced
quickly.
Apart from [~arpitagarwal] said, another way to detect slow disk is to get the
disk {{SMART}} information by script.
> HDFS Slow disk detection
> ------------------------
>
> Key: HDFS-7896
> URL: https://issues.apache.org/jira/browse/HDFS-7896
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Arpit Agarwal
>
> HDFS should detect slow disks. To start with we can flag this information via
> the NameNode web UI. Alternatively DNs can avoid using slow disks for writes.
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