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https://issues.apache.org/jira/browse/HDFS-8747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14649486#comment-14649486
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Xiaoyu Yao commented on HDFS-8747:
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Thanks [~andrew.wang] for reviewing.
bq. Have you thought about simply allowing rename between EZs with the same
settings? This would be a much smaller and easier change with similar
properties. Your proposal I think is still better in terms of ease-of-use and
also ensuring security invariants around key rolling (if/when we implement
that).
Yes. We've discussed this simpler work around. But there are many limitations
such as security invariants you mentioned above. We don't want to limit
different EZs to share the same zone key just to support rename as they may
have different policies. Encryption zone as a security concept should be
managed consistently with a single entity. Based on that, support adding
additional roots to encryption zone is a natural enhancement and better
solution.
bq. If we keep the APIs superuser-only, how does a normal user add their trash
folder to an EZ? Same for scratch folders, e.g. if the Hive user is not a
superuser.
I think we should keep this API as superuser-only. It can still be useful even
though we keep it as superuser only. The trash folder/scratch folder can be
per-created and added to encryption zone by super user as needed. This removes
the limitation for hive scratch folder, which currently has to be configured
under the single root of the encryption zone. We can discuss more on this for
HDFS-8831.
> Provide Better "Scratch Space" and "Soft Delete" Support for HDFS Encryption
> Zones
> ----------------------------------------------------------------------------------
>
> Key: HDFS-8747
> URL: https://issues.apache.org/jira/browse/HDFS-8747
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: encryption
> Affects Versions: 2.6.0
> Reporter: Xiaoyu Yao
> Assignee: Xiaoyu Yao
> Attachments: HDFS-8747-07092015.pdf, HDFS-8747-07152015.pdf,
> HDFS-8747-07292015.pdf
>
>
> HDFS Transparent Data Encryption At-Rest was introduced in Hadoop 2.6 to
> allow create encryption zone on top of a single HDFS directory. Files under
> the root directory of the encryption zone will be encrypted/decrypted
> transparently upon HDFS client write or read operations.
> Generally, it does not support rename(without data copying) across encryption
> zones or between encryption zone and non-encryption zone because different
> security settings of encryption zones. However, there are certain use cases
> where efficient rename support is desired. This JIRA is to propose better
> support of two such use cases “Scratch Space” (a.k.a. staging area) and “Soft
> Delete” (a.k.a. trash) with HDFS encryption zones.
> “Scratch Space” is widely used in Hadoop jobs, which requires efficient
> rename support. Temporary files from MR jobs are usually stored in staging
> area outside encryption zone such as “/tmp” directory and then rename to
> targeted directories as specified once the data is ready to be further
> processed.
> Below is a summary of supported/unsupported cases from latest Hadoop:
> * Rename within the encryption zone is supported
> * Rename the entire encryption zone by moving the root directory of the zone
> is allowed.
> * Rename sub-directory/file from encryption zone to non-encryption zone is
> not allowed.
> * Rename sub-directory/file from encryption zone A to encryption zone B is
> not allowed.
> * Rename from non-encryption zone to encryption zone is not allowed.
> “Soft delete” (a.k.a. trash) is a client-side “soft delete” feature that
> helps prevent accidental deletion of files and directories. If trash is
> enabled and a file or directory is deleted using the Hadoop shell, the file
> is moved to the .Trash directory of the user's home directory instead of
> being deleted. Deleted files are initially moved (renamed) to the Current
> sub-directory of the .Trash directory with original path being preserved.
> Files and directories in the trash can be restored simply by moving them to a
> location outside the .Trash directory.
> Due to the limited rename support, delete sub-directory/file within
> encryption zone with trash feature is not allowed. Client has to use
> -skipTrash option to work around this. HADOOP-10902 and HDFS-6767 improved
> the error message but without a complete solution to the problem.
> We propose to solve the problem by generalizing the mapping between
> encryption zone and its underlying HDFS directories from 1:1 today to 1:N.
> The encryption zone should allow non-overlapped directories such as scratch
> space or soft delete "trash" locations to be added/removed dynamically after
> creation. This way, rename for "scratch space" and "soft delete" can be
> better supported without breaking the assumption that rename is only
> supported "within the zone".
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