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https://issues.apache.org/jira/browse/HDFS-9826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15238589#comment-15238589
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Walter Su commented on HDFS-9826:
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Good thought. And I think current implementation {{LowRedundancyBlocks}} uses
multi-level priority queue. Blocks of highest risk are always processed first.
It achieves the same goal as you proposed. Don't you think?
> Erasure Coding: Postpone the recovery work for a configurable time period
> --------------------------------------------------------------------------
>
> Key: HDFS-9826
> URL: https://issues.apache.org/jira/browse/HDFS-9826
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Li Bo
> Assignee: Li Bo
> Attachments: HDFS-9826-001.patch, HDFS-9826-002.patch
>
>
> Currently NameNode prepares recovering when finding an under replicated
> block group. This is inefficient and reduces resources for other operations.
> It would be better to postpone the recovery work for a period of time if only
> one internal block is corrupted considering points shown by papers such as
> \[1\]\[2\]:
> 1. Transient errors in which no data are lost account for more than 90% of
> data center failures, owing to network partitions, software problems, or
> non-disk hardware faults.
> 2. Although erasure codes tolerate multiple simultaneous failures, single
> failures represent 99.75% of recoveries.
> Different clusters may have different status, so we should allow user to
> configure the time for postponing the recoveries. Proper configuration will
> reduce a large proportion of unnecessary recoveries. When finding multiple
> internal blocks corrupted in a block group, we prepare the recovery work
> immediately because it’s very rare and we don’t want to increase the risk of
> losing data.
> [1] Availability in globally distributed storage systems
> http://static.usenix.org/events/osdi10/tech/full_papers/Ford.pdf
> [2] Rethinking erasure codes for cloud file systems: minimizing I/O for
> recovery and degraded reads
> http://static.usenix.org/events/fast/tech/full_papers/Khan.pdf
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