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From "Xiaoyu Yao (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-8747) Provide Better "Scratch Space" and "Soft Delete" Support for HDFS Encryption Zones
Date Thu, 09 Jul 2015 21:59:05 GMT
Xiaoyu Yao created HDFS-8747:

             Summary: Provide Better "Scratch Space" and "Soft Delete" Support for HDFS Encryption
                 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

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 case “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

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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