HDFS-7667. Various typos and improvements to HDFS Federation doc (Charles Lamb via aw)
This commit is contained in:
Allen Wittenauer
parent
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d411460e0d
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@ -290,6 +290,9 @@ Trunk (Unreleased)
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HADOOP-11484. hadoop-mapreduce-client-nativetask fails to build on ARM
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AARCH64 due to x86 asm statements (Edward Nevill via Colin P. McCabe)
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HDFS-7667. Various typos and improvements to HDFS Federation doc
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(Charles Lamb via aw)
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Release 2.7.0 - UNRELEASED
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INCOMPATIBLE CHANGES
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@ -32,16 +32,16 @@ HDFS Federation
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* <<Namespace>>
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* Consists of directories, files and blocks
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* Consists of directories, files and blocks.
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* It supports all the namespace related file system operations such as
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create, delete, modify and list files and directories.
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* <<Block Storage Service>> has two parts
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* <<Block Storage Service>>, which has two parts:
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* Block Management (which is done in Namenode)
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* Block Management (performed in the Namenode)
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* Provides datanode cluster membership by handling registrations, and
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* Provides Datanode cluster membership by handling registrations, and
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periodic heart beats.
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* Processes block reports and maintains location of blocks.
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@ -49,29 +49,29 @@ HDFS Federation
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* Supports block related operations such as create, delete, modify and
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get block location.
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* Manages replica placement and replication of a block for under
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replicated blocks and deletes blocks that are over replicated.
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* Manages replica placement, block replication for under
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replicated blocks, and deletes blocks that are over replicated.
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* Storage - is provided by datanodes by storing blocks on the local file
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system and allows read/write access.
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* Storage - is provided by Datanodes by storing blocks on the local file
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system and allowing read/write access.
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The prior HDFS architecture allows only a single namespace for the
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entire cluster. A single Namenode manages this namespace. HDFS
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Federation addresses limitation of the prior architecture by adding
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support multiple Namenodes/namespaces to HDFS file system.
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entire cluster. In that configuration, a single Namenode manages the
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namespace. HDFS Federation addresses this limitation by adding
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support for multiple Namenodes/namespaces to HDFS.
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* {Multiple Namenodes/Namespaces}
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In order to scale the name service horizontally, federation uses multiple
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independent Namenodes/namespaces. The Namenodes are federated, that is, the
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independent Namenodes/namespaces. The Namenodes are federated; the
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Namenodes are independent and do not require coordination with each other.
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The datanodes are used as common storage for blocks by all the Namenodes.
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Each datanode registers with all the Namenodes in the cluster. Datanodes
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send periodic heartbeats and block reports and handles commands from the
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Namenodes.
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The Datanodes are used as common storage for blocks by all the Namenodes.
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Each Datanode registers with all the Namenodes in the cluster. Datanodes
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send periodic heartbeats and block reports. They also handle
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commands from the Namenodes.
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Users may use {{{./ViewFs.html}ViewFs}} to create personalized namespace views,
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where ViewFs is analogous to client side mount tables in some Unix/Linux systems.
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Users may use {{{./ViewFs.html}ViewFs}} to create personalized namespace views.
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ViewFs is analogous to client side mount tables in some Unix/Linux systems.
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[./images/federation.gif] HDFS Federation Architecture
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@ -79,66 +79,67 @@ HDFS Federation
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<<Block Pool>>
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A Block Pool is a set of blocks that belong to a single namespace.
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Datanodes store blocks for all the block pools in the cluster.
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It is managed independently of other block pools. This allows a namespace
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to generate Block IDs for new blocks without the need for coordination
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with the other namespaces. The failure of a Namenode does not prevent
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the datanode from serving other Namenodes in the cluster.
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Datanodes store blocks for all the block pools in the cluster. Each
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Block Pool is managed independently. This allows a namespace to
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generate Block IDs for new blocks without the need for coordination
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with the other namespaces. A Namenode failure does not prevent the
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Datanode from serving other Namenodes in the cluster.
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A Namespace and its block pool together are called Namespace Volume.
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It is a self-contained unit of management. When a Namenode/namespace
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is deleted, the corresponding block pool at the datanodes is deleted.
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is deleted, the corresponding block pool at the Datanodes is deleted.
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Each namespace volume is upgraded as a unit, during cluster upgrade.
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<<ClusterID>>
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A new identifier <<ClusterID>> is added to identify all the nodes in
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the cluster. When a Namenode is formatted, this identifier is provided
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or auto generated. This ID should be used for formatting the other
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Namenodes into the cluster.
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A <<ClusterID>> identifier is used to identify all the nodes in the
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cluster. When a Namenode is formatted, this identifier is either
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provided or auto generated. This ID should be used for formatting
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the other Namenodes into the cluster.
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** Key Benefits
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* Namespace Scalability - HDFS cluster storage scales horizontally but
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the namespace does not. Large deployments or deployments using lot
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of small files benefit from scaling the namespace by adding more
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Namenodes to the cluster
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* Namespace Scalability - Federation adds namespace horizontal
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scaling. Large deployments or deployments using lot of small files
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benefit from namespace scaling by allowing more Namenodes to be
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added to the cluster.
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* Performance - File system operation throughput is limited by a single
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Namenode in the prior architecture. Adding more Namenodes to the cluster
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scales the file system read/write operations throughput.
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* Performance - File system throughput is not limited by a single
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Namenode. Adding more Namenodes to the cluster scales the file
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system read/write throughput.
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* Isolation - A single Namenode offers no isolation in multi user
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environment. An experimental application can overload the Namenode
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and slow down production critical applications. With multiple Namenodes,
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different categories of applications and users can be isolated to
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different namespaces.
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* Isolation - A single Namenode offers no isolation in a multi user
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environment. For example, an experimental application can overload
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the Namenode and slow down production critical applications. By using
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multiple Namenodes, different categories of applications and users
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can be isolated to different namespaces.
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* {Federation Configuration}
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Federation configuration is <<backward compatible>> and allows existing
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single Namenode configuration to work without any change. The new
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configuration is designed such that all the nodes in the cluster have
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same configuration without the need for deploying different configuration
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based on the type of the node in the cluster.
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Federation configuration is <<backward compatible>> and allows
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existing single Namenode configurations to work without any
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change. The new configuration is designed such that all the nodes in
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the cluster have the same configuration without the need for
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deploying different configurations based on the type of the node in
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the cluster.
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A new abstraction called <<<NameServiceID>>> is added with
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federation. The Namenode and its corresponding secondary/backup/checkpointer
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nodes belong to this. To support single configuration file, the Namenode and
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secondary/backup/checkpointer configuration parameters are suffixed with
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<<<NameServiceID>>> and are added to the same configuration file.
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Federation adds a new <<<NameServiceID>>> abstraction. A Namenode
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and its corresponding secondary/backup/checkpointer nodes all belong
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to a NameServiceId. In order to support a single configuration file,
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the Namenode and secondary/backup/checkpointer configuration
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parameters are suffixed with the <<<NameServiceID>>>.
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** Configuration:
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<<Step 1>>: Add the following parameters to your configuration:
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<<<dfs.nameservices>>>: Configure with list of comma separated
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NameServiceIDs. This will be used by Datanodes to determine all the
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<<Step 1>>: Add the <<<dfs.nameservices>>> parameter to your
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configuration and configure it with a list of comma separated
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NameServiceIDs. This will be used by the Datanodes to determine the
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Namenodes in the cluster.
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<<Step 2>>: For each Namenode and Secondary Namenode/BackupNode/Checkpointer
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add the following configuration suffixed with the corresponding
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<<<NameServiceID>>> into the common configuration file.
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add the following configuration parameters suffixed with the corresponding
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<<<NameServiceID>>> into the common configuration file:
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*---------------------+--------------------------------------------+
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|| Daemon || Configuration Parameter |
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@ -160,7 +161,7 @@ HDFS Federation
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| | <<<dfs.secondary.namenode.keytab.file>>> |
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*---------------------+--------------------------------------------+
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Here is an example configuration with two namenodes:
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Here is an example configuration with two Namenodes:
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----
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<configuration>
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@ -199,16 +200,16 @@ HDFS Federation
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** Formatting Namenodes
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<<Step 1>>: Format a namenode using the following command:
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<<Step 1>>: Format a Namenode using the following command:
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----
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs namenode -format [-clusterId <cluster_id>]
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----
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Choose a unique cluster_id, which will not conflict other clusters in
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your environment. If it is not provided, then a unique ClusterID is
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Choose a unique cluster_id which will not conflict other clusters in
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your environment. If a cluster_id is not provided, then a unique one is
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auto generated.
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<<Step 2>>: Format additional namenode using the following command:
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<<Step 2>>: Format additional Namenodes using the following command:
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----
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs namenode -format -clusterId <cluster_id>
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@ -219,40 +220,38 @@ HDFS Federation
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** Upgrading from an older release and configuring federation
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Older releases supported a single Namenode.
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Upgrade the cluster to newer release to enable federation
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Older releases only support a single Namenode.
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Upgrade the cluster to newer release in order to enable federation
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During upgrade you can provide a ClusterID as follows:
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----
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs start namenode --config $HADOOP_CONF_DIR -upgrade -clusterId <cluster_ID>
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs --daemon start namenode -upgrade -clusterId <cluster_ID>
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----
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If ClusterID is not provided, it is auto generated.
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If cluster_id is not provided, it is auto generated.
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** Adding a new Namenode to an existing HDFS cluster
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Follow the following steps:
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Perform the following steps:
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* Add configuration parameter <<<dfs.nameservices>>> to the configuration.
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* Add <<<dfs.nameservices>>> to the configuration.
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* Update the configuration with NameServiceID suffix. Configuration
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key names have changed post release 0.20. You must use new configuration
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parameter names, for federation.
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* Update the configuration with the NameServiceID suffix. Configuration
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key names changed post release 0.20. You must use the new configuration
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parameter names in order to use federation.
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* Add new Namenode related config to the configuration files.
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* Add the new Namenode related config to the configuration file.
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* Propagate the configuration file to the all the nodes in the cluster.
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* Start the new Namenode, Secondary/Backup.
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* Start the new Namenode and Secondary/Backup.
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* Refresh the datanodes to pickup the newly added Namenode by running
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the following command:
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* Refresh the Datanodes to pickup the newly added Namenode by running
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the following command against all the Datanodes in the cluster:
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----
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs dfadmin -refreshNameNode <datanode_host_name>:<datanode_rpc_port>
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs dfsadmin -refreshNameNode <datanode_host_name>:<datanode_rpc_port>
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----
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* The above command must be run against all the datanodes in the cluster.
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* {Managing the cluster}
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** Starting and stopping cluster
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@ -270,28 +269,28 @@ HDFS Federation
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----
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These commands can be run from any node where the HDFS configuration is
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available. The command uses configuration to determine the Namenodes
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in the cluster and starts the Namenode process on those nodes. The
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datanodes are started on nodes specified in the <<<slaves>>> file. The
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script can be used as reference for building your own scripts for
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starting and stopping the cluster.
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available. The command uses the configuration to determine the Namenodes
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in the cluster and then starts the Namenode process on those nodes. The
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Datanodes are started on the nodes specified in the <<<slaves>>> file. The
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script can be used as a reference for building your own scripts to
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start and stop the cluster.
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** Balancer
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Balancer has been changed to work with multiple Namenodes in the cluster to
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balance the cluster. Balancer can be run using the command:
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The Balancer has been changed to work with multiple
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Namenodes. The Balancer can be run using the command:
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----
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[hdfs]$ $HADOOP_PREFIX/bin/hdfs --daemon start balancer [-policy <policy>]
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----
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Policy could be:
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The policy parameter can be any of the following:
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* <<<datanode>>> - this is the <default> policy. This balances the storage at
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the datanode level. This is similar to balancing policy from prior releases.
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the Datanode level. This is similar to balancing policy from prior releases.
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* <<<blockpool>>> - this balances the storage at the block pool level.
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Balancing at block pool level balances storage at the datanode level also.
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* <<<blockpool>>> - this balances the storage at the block pool
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level which also balances at the Datanode level.
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Note that Balancer only balances the data and does not balance the namespace.
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For the complete command usage, see {{{../hadoop-common/CommandsManual.html#balancer}balancer}}.
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@ -299,44 +298,42 @@ HDFS Federation
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** Decommissioning
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Decommissioning is similar to prior releases. The nodes that need to be
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decomissioned are added to the exclude file at all the Namenode. Each
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decomissioned are added to the exclude file at all of the Namenodes. Each
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Namenode decommissions its Block Pool. When all the Namenodes finish
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decommissioning a datanode, the datanode is considered to be decommissioned.
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decommissioning a Datanode, the Datanode is considered decommissioned.
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<<Step 1>>: To distributed an exclude file to all the Namenodes, use the
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<<Step 1>>: To distribute an exclude file to all the Namenodes, use the
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following command:
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----
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[hdfs]$ $HADOOP_PREFIX/sbin/distributed-exclude.sh <exclude_file>
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[hdfs]$ $HADOOP_PREFIX/sbin/distribute-exclude.sh <exclude_file>
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----
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<<Step 2>>: Refresh all the Namenodes to pick up the new exclude file.
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<<Step 2>>: Refresh all the Namenodes to pick up the new exclude file:
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----
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[hdfs]$ $HADOOP_PREFIX/sbin/refresh-namenodes.sh
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----
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The above command uses HDFS configuration to determine the Namenodes
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configured in the cluster and refreshes all the Namenodes to pick up
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The above command uses HDFS configuration to determine the
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configured Namenodes in the cluster and refreshes them to pick up
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the new exclude file.
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** Cluster Web Console
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Similar to Namenode status web page, a Cluster Web Console is added in
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federation to monitor the federated cluster at
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Similar to the Namenode status web page, when using federation a
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Cluster Web Console is available to monitor the federated cluster at
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<<<http://<any_nn_host:port>/dfsclusterhealth.jsp>>>.
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Any Namenode in the cluster can be used to access this web page.
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The web page provides the following information:
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The Cluster Web Console provides the following information:
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* Cluster summary that shows number of files, number of blocks and
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total configured storage capacity, available and used storage information
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* A cluster summary that shows the number of files, number of blocks,
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total configured storage capacity, and the available and used storage
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for the entire cluster.
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* Provides list of Namenodes and summary that includes number of files,
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blocks, missing blocks, number of live and dead data nodes for each
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Namenode. It also provides a link to conveniently access Namenode web UI.
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* It also provides decommissioning status of datanodes.
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* A list of Namenodes and a summary that includes the number of files,
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blocks, missing blocks, and live and dead data nodes for each
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Namenode. It also provides a link to access each Namenode's web UI.
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* The decommissioning status of Datanodes.
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