Synonyms

Archive storage; Cloud storage; Key-value storage; Object storage

Definition

A RESTful protocol-based interface that is used to access storage in the form of objects.

Main Text

Traditional network attached protocols (NAS) provide support for POSIX semantics. Supporting POSIX makes the NAS protocols quite complex to both understand and implement. In comparison, the object protocol provides a RESTful interface (simple get and put operations) where typically one does not update an object. Instead, every update usually leads towards the creation of a new object. Object storage protocols do not adhere to POSIX semantics. Key-value interface is a specific form of object protocol where the value corresponds to an object. The underlying architecture for implementing a storage system that supports small objects (few kilobytes) is fundamentally very different than a storage system that has been designed for supporting large (mega or gigabytes) objects. Typically, a storage system that supports an object protocol maps the objects to the underlying blocks of a disk system. However, attempts have been made to design disks that natively understand objects but these systems have not gained much traction.

Scale-out systems that consist of a cluster of directly attached disk-based servers typically support an object storage protocol. It is important to note that a scale-out storage system can also support file or block based access protocols. These scale-out systems have a different design center in that they employ newer erasure coding algorithms for reliability instead of using the traditional RAID-5 algorithm. They also employ an eventual consistency model to keep the meta-data consistent across all of the nodes unlike a more traditional storage controller that employs strong consistency protocols to keep the meta-data consistent across the cluster of storage nodes.

In conclusion, storage industry is experiencing dramatic changes with respect to the new types of protocols being used to access storage (object, key-value store), new types of storage architectures (SSD-based performance optimized storage, and capacity optimized scale-out storage architectures), and the use of new types of persistent media (flash, PCM, STT-MRAM, NRAM).