According to relevant public information, HashMap is a Chinese name HashMap. HashMap is a collection of key-value pairs, each key-value pair is also called Entry, and objects are saved in the form of key-value pairs.

Object is the basic unit of data storage in the system. An object is a combination of file data and a set of attribute information, which can define file-based RAID parameters, data distribution and quality of service. However, in traditional storage systems, files or blocks are used as basic storage units. In the block storage system, it is necessary to keep track of the properties of each block in the system, and the object maintains its own properties by communicating with the storage system.

Object storage device

1. data storage: OSD manages object data and puts them on a standard disk system. OSD does not provide block interface access, and the client reads and writes data with object ID and offset when requesting data.

2. Intelligent distribution: OSD uses its own CPU and memory to optimize data distribution and support data prefetching. Because OSD can intelligently support object prefetching, it can optimize the performance of the disk.

3. Metadata management of each object: OSD manages the metadata of the objects stored on it, which is similar to the traditional inode metadata and usually includes the length of data blocks and objects. In the traditional NAS system, these metadata are maintained by the file server, and the object storage architecture completes the main metadata management in the system through OSD, which reduces the overhead of the client.