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https://issues.apache.org/jira/browse/HDFS-8415?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15028276#comment-15028276
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Zhe Zhang commented on HDFS-8415:
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[~szetszwo] I think the upsides are similar to the upsides of RAID5 (rotating
parity) compared to RAID3. Quoting from Wikipedia:
{quote}
In comparison to RAID 4, RAID 5's distributed parity evens out the stress of a
dedicated parity disk among all RAID members. Additionally, read performance is
increased since all RAID members participate in serving of the read requests.
{quote}
If we rotate the role of data / parity blocks for each stripe of cells, then
we'll be reading from {{DN0, DN1, DN2, DN3, DN4, DN5}} for the 1st stripe, and
{{DN1, DN2, DN3, DN4, DN5, DN6}} for the 2nd stripe. In theory this could
leverage 9 disk spindles in parallel, instead of 6 without rotation.
The downside is the added complexity.
> Erasure coding: rotated parity placement (RAID5/6)
> --------------------------------------------------
>
> Key: HDFS-8415
> URL: https://issues.apache.org/jira/browse/HDFS-8415
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Zhe Zhang
> Assignee: Zhe Zhang
>
> Our current implementation uses fixed internal blocks for parity data,
> similar to RAID3. Rotated parity placement like RAID5/6 has interesting
> tradeoffs that we should investigate.
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