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Posted to hdfs-issues@hadoop.apache.org by "Walter Su (JIRA)" <ji...@apache.org> on 2016/04/13 06:29:25 UTC
[jira] [Commented] (HDFS-9826) Erasure Coding: Postpone the
recovery work for a configurable time period
[ https://issues.apache.org/jira/browse/HDFS-9826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15238589#comment-15238589 ]
Walter Su commented on HDFS-9826:
---------------------------------
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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