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https://issues.apache.org/jira/browse/HDFS-7068?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14352558#comment-14352558
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Walter Su commented on HDFS-7068:
---------------------------------
I think putting block placement policy selection strategy into StoragePolicy is
not a good idea.
First, placementPolicy selection and StorageType selection are orthogonal.
Second, StoragePolicy is used by block placement policy. If we use
StoragePolicy to select block placement policy. These two classes are tangled.
In the patch, I hard coded selection schema. Maybe we can add a property like
<name> placemenPolicy.schema [/name]
<value> [default]com.package.DefaultPolicy,
[XOR]com.package.FaultTolarentPolicy, [RS]com.package.FaultTolarentPolicy
</value>
> Support multiple block placement policies
> -----------------------------------------
>
> Key: HDFS-7068
> URL: https://issues.apache.org/jira/browse/HDFS-7068
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 2.5.1
> Reporter: Zesheng Wu
> Assignee: Walter Su
> Attachments: HDFS-7068.patch
>
>
> According to the code, the current implement of HDFS only supports one
> specific type of block placement policy, which is BlockPlacementPolicyDefault
> by default.
> The default policy is enough for most of the circumstances, but under some
> special circumstances, it works not so well.
> For example, on a shared cluster, we want to erasure encode all the files
> under some specified directories. So the files under these directories need
> to use a new placement policy.
> But at the same time, other files still use the default placement policy.
> Here we need to support multiple placement policies for the HDFS.
> One plain thought is that, the default placement policy is still configured
> as the default. On the other hand, HDFS can let user specify customized
> placement policy through the extended attributes(xattr). When the HDFS choose
> the replica targets, it firstly check the customized placement policy, if not
> specified, it fallbacks to the default one.
> Any thoughts?
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