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https://issues.apache.org/jira/browse/HDFS-7584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14286520#comment-14286520
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Zhe Zhang commented on HDFS-7584:
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This is a very useful feature and thanks [~xyao] for initiating the work. A few
comments:
# bq. For example, when SSD is not available but Quota of SSD is available, the
write will fallback to DISK and the storage usage deducted from both SSD and
the cumulative disk space quota of the directory even no SSD space is being
consumed.
This is an interesting scenario and is worth more discussion. It is a
conservative and safe policy to deduct from both SSD and DISK quotas. However
it doesn't fully comply with the principle of _quota based on intended usage_,
which might make it appear counter-intuitive to users (e.g. why am I double
charged?). As an extreme example, what if the user doesn't have any DISK quota?
# How about calculating quota truly based on intended usage? The charged quota
might be different than the usage, but so is the case with existing quota
logic. What are other disadvantages?
# If we do want to charge by actual usage (5.2), maybe we should allow
different "quota currencies" to be exchanged? Something like 1GB of SSD = 2GB
of DISK = 4GB of ARCHIVAL. Or at least allow a user with _only_ 1GB SSD quota
to use 1GB DISK space.
> Enable Quota Support for Storage Types (SSD)
> ---------------------------------------------
>
> Key: HDFS-7584
> URL: https://issues.apache.org/jira/browse/HDFS-7584
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode, namenode
> Reporter: Xiaoyu Yao
> Assignee: Xiaoyu Yao
> Attachments: HDFS-7584 Quota by Storage Type - 01202015.pdf
>
>
> Phase II of the Heterogeneous storage features have completed by HDFS-6584.
> This JIRA is opened to enable Quota support of different storage types in
> terms of storage space usage. This is more important for certain storage
> types such as SSD as it is precious and more performant.
> As described in the design doc of HDFS-5682, we plan to add new
> quotaByStorageType command and new name node RPC protocol for it. The quota
> by storage type feature is applied to HDFS directory level similar to
> traditional HDFS space quota.
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