HADOOP-14491. Azure has messed doc structure. Contributed by Mingliang Liu
(cherry picked from commit 536f057158)
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Mingliang Liu
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@ -14,20 +14,9 @@
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# Hadoop Azure Support: Azure Blob Storage
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* [Introduction](#Introduction)
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* [Features](#Features)
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* [Limitations](#Limitations)
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* [Usage](#Usage)
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* [Concepts](#Concepts)
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* [Configuring Credentials](#Configuring_Credentials)
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* [Page Blob Support and Configuration](#Page_Blob_Support_and_Configuration)
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* [Atomic Folder Rename](#Atomic_Folder_Rename)
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* [Accessing wasb URLs](#Accessing_wasb_URLs)
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* [Append API Support and Configuration](#Append_API_Support_and_Configuration)
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* [Multithread Support](#Multithread_Support)
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* [Testing the hadoop-azure Module](#Testing_the_hadoop-azure_Module)
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<!-- MACRO{toc|fromDepth=1|toDepth=3} -->
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## <a name="Introduction" />Introduction
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## Introduction
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The hadoop-azure module provides support for integration with
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[Azure Blob Storage](http://azure.microsoft.com/en-us/documentation/services/storage/).
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@ -35,7 +24,7 @@ The built jar file, named hadoop-azure.jar, also declares transitive dependencie
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on the additional artifacts it requires, notably the
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[Azure Storage SDK for Java](https://github.com/Azure/azure-storage-java).
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## <a name="Features" />Features
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## Features
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* Read and write data stored in an Azure Blob Storage account.
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* Present a hierarchical file system view by implementing the standard Hadoop
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@ -51,15 +40,15 @@ on the additional artifacts it requires, notably the
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* Tested on both Linux and Windows.
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* Tested at scale.
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## <a name="Limitations" />Limitations
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## Limitations
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* File owner and group are persisted, but the permissions model is not enforced.
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Authorization occurs at the level of the entire Azure Blob Storage account.
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* File last access time is not tracked.
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## <a name="Usage" />Usage
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## Usage
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### <a name="Concepts" />Concepts
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### Concepts
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The Azure Blob Storage data model presents 3 core concepts:
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@ -73,7 +62,7 @@ The Azure Blob Storage data model presents 3 core concepts:
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The internal implementation also uses blobs to persist the file system
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hierarchy and other metadata.
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### <a name="Configuring_Credentials" />Configuring Credentials
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### Configuring Credentials
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Usage of Azure Blob Storage requires configuration of credentials. Typically
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this is set in core-site.xml. The configuration property name is of the form
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@ -84,11 +73,12 @@ untrusted party.**
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For example:
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<property>
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<name>fs.azure.account.key.youraccount.blob.core.windows.net</name>
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<value>YOUR ACCESS KEY</value>
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</property>
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```xml
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<property>
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<name>fs.azure.account.key.youraccount.blob.core.windows.net</name>
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<value>YOUR ACCESS KEY</value>
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</property>
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```
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In many Hadoop clusters, the core-site.xml file is world-readable. It is possible to
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protect the access key within a credential provider as well. This provides an encrypted
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file format along with protection with file permissions.
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@ -107,14 +97,14 @@ For additional reading on the credential provider API see:
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###### provision
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```
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```bash
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% hadoop credential create fs.azure.account.key.youraccount.blob.core.windows.net -value 123
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-provider localjceks://file/home/lmccay/wasb.jceks
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```
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###### configure core-site.xml or command line system property
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```
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```xml
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<property>
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<name>hadoop.security.credential.provider.path</name>
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<value>localjceks://file/home/lmccay/wasb.jceks</value>
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@ -124,7 +114,7 @@ For additional reading on the credential provider API see:
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###### distcp
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```
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```bash
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% hadoop distcp
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[-D hadoop.security.credential.provider.path=localjceks://file/home/lmccay/wasb.jceks]
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hdfs://hostname:9001/user/lmccay/007020615 wasb://yourcontainer@youraccount.blob.core.windows.net/testDir/
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@ -142,22 +132,25 @@ specifies an external program to be invoked by Hadoop processes to decrypt the
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key. The encrypted key value is passed to this external program as a command
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line argument:
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<property>
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<name>fs.azure.account.keyprovider.youraccount</name>
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<value>org.apache.hadoop.fs.azure.ShellDecryptionKeyProvider</value>
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</property>
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```xml
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<property>
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<name>fs.azure.account.keyprovider.youraccount</name>
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<value>org.apache.hadoop.fs.azure.ShellDecryptionKeyProvider</value>
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</property>
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<property>
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<name>fs.azure.account.key.youraccount.blob.core.windows.net</name>
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<value>YOUR ENCRYPTED ACCESS KEY</value>
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</property>
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<property>
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<name>fs.azure.account.key.youraccount.blob.core.windows.net</name>
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<value>YOUR ENCRYPTED ACCESS KEY</value>
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</property>
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<property>
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<name>fs.azure.shellkeyprovider.script</name>
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<value>PATH TO DECRYPTION PROGRAM</value>
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</property>
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<property>
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<name>fs.azure.shellkeyprovider.script</name>
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<value>PATH TO DECRYPTION PROGRAM</value>
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</property>
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### <a name="Page_Blob_Support_and_Configuration" />Page Blob Support and Configuration
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```
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### Page Blob Support and Configuration
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The Azure Blob Storage interface for Hadoop supports two kinds of blobs,
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[block blobs and page blobs](http://msdn.microsoft.com/en-us/library/azure/ee691964.aspx).
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@ -179,10 +172,12 @@ folder names.
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For example:
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<property>
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<name>fs.azure.page.blob.dir</name>
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<value>/hbase/WALs,/hbase/oldWALs,/data/mypageblobfiles</value>
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</property>
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```xml
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<property>
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<name>fs.azure.page.blob.dir</name>
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<value>/hbase/WALs,/hbase/oldWALs,/data/mypageblobfiles</value>
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</property>
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```
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You can set this to simply / to make all files page blobs.
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@ -194,7 +189,7 @@ The configuration option `fs.azure.page.blob.extension.size` is the page blob
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extension size. This defines the amount to extend a page blob if it starts to
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get full. It must be 128MB or greater, specified as an integer number of bytes.
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### <a name="Atomic_Folder_Rename" />Atomic Folder Rename
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### Atomic Folder Rename
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Azure storage stores files as a flat key/value store without formal support
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for folders. The hadoop-azure file system layer simulates folders on top
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@ -213,12 +208,14 @@ the intention of the rename operation, to allow redo in event of a failure.
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For example:
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<property>
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<name>fs.azure.atomic.rename.dir</name>
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<value>/hbase,/data</value>
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</property>
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```xml
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<property>
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<name>fs.azure.atomic.rename.dir</name>
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<value>/hbase,/data</value>
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</property>
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```
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### <a name="Accessing_wasb_URLs" />Accessing wasb URLs
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### Accessing wasb URLs
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After credentials are configured in core-site.xml, any Hadoop component may
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reference files in that Azure Blob Storage account by using URLs of the following
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@ -235,28 +232,32 @@ For example, the following
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commands demonstrate access to a storage account named `youraccount` and a
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container named `yourcontainer`.
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> hadoop fs -mkdir wasb://yourcontainer@youraccount.blob.core.windows.net/testDir
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```bash
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% hadoop fs -mkdir wasb://yourcontainer@youraccount.blob.core.windows.net/testDir
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> hadoop fs -put testFile wasb://yourcontainer@youraccount.blob.core.windows.net/testDir/testFile
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% hadoop fs -put testFile wasb://yourcontainer@youraccount.blob.core.windows.net/testDir/testFile
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> hadoop fs -cat wasbs://yourcontainer@youraccount.blob.core.windows.net/testDir/testFile
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test file content
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% hadoop fs -cat wasbs://yourcontainer@youraccount.blob.core.windows.net/testDir/testFile
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test file content
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```
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It's also possible to configure `fs.defaultFS` to use a `wasb` or `wasbs` URL.
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This causes all bare paths, such as `/testDir/testFile` to resolve automatically
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to that file system.
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### <a name="Append_API_Support_and_Configuration" />Append API Support and Configuration
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### Append API Support and Configuration
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The Azure Blob Storage interface for Hadoop has optional support for Append API for
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single writer by setting the configuration `fs.azure.enable.append.support` to true.
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For Example:
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<property>
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<name>fs.azure.enable.append.support</name>
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<value>true</value>
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</property>
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```xml
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<property>
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<name>fs.azure.enable.append.support</name>
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<value>true</value>
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</property>
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```
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It must be noted Append support in Azure Blob Storage interface DIFFERS FROM HDFS SEMANTICS. Append
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support does not enforce single writer internally but requires applications to guarantee this semantic.
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file path, or rely on some external locking mechanism of its own. Failure to do so will result in
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unexpected behavior.
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### <a name="Multithread_Support" />Multithread Support
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### Multithread Support
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Rename and Delete blob operations on directories with large number of files and sub directories currently is very slow as these operations are done one blob at a time serially. These files and sub folders can be deleted or renamed parallel. Following configurations can be used to enable threads to do parallel processing
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To enable 10 threads for Delete operation. Set configuration value to 0 or 1 to disable threads. The default behavior is threads disabled.
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<property>
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<name>fs.azure.delete.threads</name>
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<value>10</value>
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</property>
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```xml
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<property>
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<name>fs.azure.delete.threads</name>
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<value>10</value>
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</property>
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```
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To enable 20 threads for Rename operation. Set configuration value to 0 or 1 to disable threads. The default behavior is threads disabled.
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<property>
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<name>fs.azure.rename.threads</name>
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<value>20</value>
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</property>
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```xml
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<property>
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<name>fs.azure.rename.threads</name>
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<value>20</value>
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</property>
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```
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### <a name="WASB_SECURE_MODE" />WASB Secure mode and configuration
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### WASB Secure mode and configuration
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WASB can operate in secure mode where the Storage access keys required to communicate with Azure storage does not have to
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be in the same address space as the process using WASB. In this mode all interactions with Azure storage is performed using
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@ -292,30 +297,32 @@ Romote mode, however for testing purposes the local mode can be enabled to gener
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To enable Secure mode following property needs to be set to true.
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```
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<property>
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<name>fs.azure.secure.mode</name>
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<value>true</value>
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</property>
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```xml
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<property>
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<name>fs.azure.secure.mode</name>
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<value>true</value>
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</property>
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```
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To enable SAS key generation locally following property needs to be set to true.
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```xml
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<property>
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<name>fs.azure.local.sas.key.mode</name>
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<value>true</value>
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</property>
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```
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<property>
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<name>fs.azure.local.sas.key.mode</name>
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<value>true</value>
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</property>
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```
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To use the remote SAS key generation mode, an external REST service is expected to provided required SAS keys.
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Following property can used to provide the end point to use for remote SAS Key generation:
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```xml
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<property>
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<name>fs.azure.cred.service.url</name>
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<value>{URL}</value>
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</property>
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```
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<property>
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<name>fs.azure.cred.service.url</name>
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<value>{URL}</value>
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</property>
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```
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The remote service is expected to provide support for two REST calls ```{URL}/GET_CONTAINER_SAS``` and ```{URL}/GET_RELATIVE_BLOB_SAS```, for generating
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container and relative blob sas keys. An example requests
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@ -323,7 +330,8 @@ container and relative blob sas keys. An example requests
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```{URL}/GET_CONTAINER_SAS?storage_account=<account_name>&container=<container>&relative_path=<relative path>&sas_expiry=<expiry period>&delegation_token=<delegation token>```
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The service is expected to return a response in JSON format:
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```
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```json
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{
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"responseCode" : 0 or non-zero <int>,
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"responseMessage" : relavant message on failure <String>,
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@ -331,40 +339,42 @@ The service is expected to return a response in JSON format:
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}
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```
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## <a name="WASB Authorization" />Authorization Support in WASB.
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### Authorization Support in WASB
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Authorization support can be enabled in WASB using the following configuration:
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```
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<property>
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<name>fs.azure.authorization</name>
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<value>true</value>
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</property>
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```
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The current implementation of authorization relies on the presence of an external service that can enforce
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the authorization. The service is expected to be running on a URL provided by the following config.
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```
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<property>
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<name>fs.azure.authorization.remote.service.url</name>
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<value>{URL}</value>
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</property>
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```xml
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<property>
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<name>fs.azure.authorization</name>
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<value>true</value>
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</property>
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```
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The remote service is expected to provide support for the following REST call: ```{URL}/CHECK_AUTHORIZATION```
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An example request:
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The current implementation of authorization relies on the presence of an external service that can enforce
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the authorization. The service is expected to be running on a URL provided by the following config.
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```xml
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<property>
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<name>fs.azure.authorization.remote.service.url</name>
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<value>{URL}</value>
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</property>
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```
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The remote service is expected to provide support for the following REST call: ```{URL}/CHECK_AUTHORIZATION```
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An example request:
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```{URL}/CHECK_AUTHORIZATION?wasb_absolute_path=<absolute_path>&operation_type=<operation type>&delegation_token=<delegation token>```
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The service is expected to return a response in JSON format:
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```
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{
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The service is expected to return a response in JSON format:
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```json
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{
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"responseCode" : 0 or non-zero <int>,
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"responseMessage" : relevant message on failure <String>,
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"authorizationResult" : true/false <boolean>
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}
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```
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}
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```
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## <a name="Testing_the_hadoop-azure_Module" />Testing the hadoop-azure Module
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## Testing the hadoop-azure Module
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The hadoop-azure module includes a full suite of unit tests. Most of the tests
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will run without additional configuration by running `mvn test`. This includes
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@ -379,10 +389,12 @@ that runs on a local machine.
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To use the emulator, install Azure SDK 2.3 and start the storage emulator. Then,
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edit `src/test/resources/azure-test.xml` and add the following property:
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<property>
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<name>fs.azure.test.emulator</name>
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<value>true</value>
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</property>
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```xml
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<property>
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<name>fs.azure.test.emulator</name>
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<value>true</value>
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</property>
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```
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There is a known issue when running tests with the emulator. You may see the
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following failure message:
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@ -396,6 +408,7 @@ file to `src/test/resources/azure-auth-keys.xml` and setting
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the name of the storage account and its access key.
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For example:
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```xml
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<?xml version="1.0"?>
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<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
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