9.3 How data is stored and retrieved from Object based Storage Systems

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Unlike SAN and NAS storage systems where data is accessed through block and file level respectively, Object based storage systems stores and retrieves any application data in the form of objects and their object ID’s. Object-based storage systems has two common implementation options – software based and hardware based implementations
 
Software-based: In this option, the object storage software is installed on any compatible hardware (generally a server). It provides the flexibility to reuse the existing IT infrastructure including servers and file-based or SAN-based storage. Some vendors offer a solution where the object storage software can also be installed on virtual machines that acts as nodes and enables to leverage the existing storage.
 
Hardware-based: In this option, the object storage software is installed on purpose-built hardware, and typically pre-configured and pre-tested by the vendor. Hardware-based object storage provides better performance compared to software based implementations.

Object-based storage device stores and retrieves data in the form of objects on flat address space based on its content and other attributes rather than the file name and the location. Each object stored in the object-based storage system is identified by a unique identifier called the object ID. The object ID allows easy access to objects without the need to specify the storage location

How data is stored in the Object based Storage Systems

 
Storing data in OSD
1) The application server presents the data to be stored to the OSD node.
2) The OSD node divides the data into two parts: user data and metadata.
 
3) The OSD node generates the object ID using a specialized algorithm. The algorithm is executed against the contents of the user data to derive an ID unique to this data.
 
4) For future access, the OSD node stores the metadata and object ID using the metadata service.
 
5) The OSD node stores the user data (objects) in the storage device using the storage service.
 
6) An acknowledgement is sent to the application server stating that the object is stored. In some implementations, where the metadata service is running inside an application server, the object ID is returned back to the application server.

How data is retrieved from the Object based Storage Systems

The following steps will be taken place when retrieving the application or user data from an OSD system.

Retrieving data from OSD
1) The application server sends a read request to the OSD system.
 
2) The metadata service retrieves the object ID for the requested data.
 
3) The metadata service sends the object ID to the application server.
 
4) The application server sends the object ID to the OSD storage service for object retrieval.
 
5) The OSD storage service retrieves the object from the storage device.
 
6) The OSD storage service sends the data to the application server.

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