[HDFS-10285] Storage Policy Satisfier in HDFS

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: HDFS-10285
• Fix Version/s: HDFS-10285, 3.2.0
• Component/s: datanode, namenode

Release Note

StoragePolicySatisfier(SPS) allows users to track and satisfy the storage policy requirement of a given file/directory in HDFS. User can specify a file/directory path by invoking “hdfs storagepolicies -satisfyStoragePolicy -path <path>” command or via HdfsAdmin#satisfyStoragePolicy(path) API. For the blocks which has storage policy mismatches, it moves the replicas to a different storage type in order to fulfill the storage policy requirement. Since API calls goes to NN for tracking the invoked satisfier path(iNodes), administrator need to enable dfs.storage.policy.satisfier.mode’ config at NN to allow these operations. It can be enabled by setting ‘dfs.storage.policy.satisfier.mode’ to ‘external’ in hdfs-site.xml. The configs can be disabled dynamically without restarting Namenode. SPS should be started outside Namenode using "hdfs --daemon start sps". If administrator is looking to run Mover tool explicitly, then he/she should make sure to disable SPS first and then run Mover. See the "Storage Policy Satisfier (SPS)" section in the Archival Storage guide for detailed usage.

• Assignee: Uma Maheswara Rao G
• Reporter: Uma Maheswara Rao G
• Created: 14/Apr/16 02:21
• Updated: 21/Sep/18 11:43
• Resolved: 21/Sep/18 11:38

Description

Heterogeneous storage in HDFS introduced the concept of storage policy. These policies can be set on directory/file to specify the user preference, where to store the physical block. When user set the storage policy before writing data, then the blocks could take advantage of storage policy preferences and stores physical block accordingly.

If user set the storage policy after writing and completing the file, then the blocks would have been written with default storage policy (nothing but DISK). User has to run the ‘Mover tool’ explicitly by specifying all such file names as a list. In some distributed system scenarios (ex: HBase) it would be difficult to collect all the files and run the tool as different nodes can write files separately and file can have different paths.

Another scenarios is, when user rename the files from one effected storage policy file (inherited policy from parent directory) to another storage policy effected directory, it will not copy inherited storage policy from source. So it will take effect from destination file/dir parent storage policy. This rename operation is just a metadata change in Namenode. The physical blocks still remain with source storage policy.

So, Tracking all such business logic based file names could be difficult for admins from distributed nodes(ex: region servers) and running the Mover tool.

Here the proposal is to provide an API from Namenode itself for trigger the storage policy satisfaction. A Daemon thread inside Namenode should track such calls and process to DN as movement commands.

Will post the detailed design thoughts document soon.

Issue Links

• is depended upon by: HDFS-12226 Follow-on work for Storage Policy Satisfier in Namenode
• relates to: HDFS-11257 Evacuate DN when the remaining is negative

Sub-Tasks

• [SPS]: allow re-satisfy path after restarting sps process: Open