Block-level storage is a concept in cloud-hosted

data persistence In computing, a persistent data structure or not ephemeral data structure is a data structure that always preserves the previous version of itself when it is modified. Such data structures are effectively immutable, as their operations do not (v ...

where cloud services emulate the behaviour of a traditional

block device In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow a ...

, such as a physical

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...

. Storage in such services is organised as

block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...

s. This emulates the type of behaviour seen in traditional disks or tape storage through

storage virtualization In computer science, storage virtualization is "the process of presenting a logical view of the physical storage resources to" a host computer system, "treating all storage media (hard disk, optical disk, tape, etc.) in the enterprise as a singl ...

. Blocks are identified by an arbitrary and assigned identifier by which they may be stored and retrieved, but this has no obvious meaning in terms of files or documents. A file system must be applied on top of the block-level storage to map 'files' onto a sequence of blocks. Amazon EBS (elastic block store) is an example of a cloud block store. Cloud block-level storage will usually offer facilities such as replication for reliability, or backup services. Block-level storage is in contrast to an object store or 'bucket store', such as

Amazon S3 Amazon S3 or Amazon Simple Storage Service is a service offered by Amazon Web Services (AWS) that provides object storage through a web service interface. Amazon S3 uses the same scalable storage infrastructure that Amazon.com uses to run its ...

(simple storage service), or to a database. These operate at a higher level of abstraction and are able to work with entities such as files, documents, images, videos or database records. Instance stores are another form of cloud-hosted block-level storage. These are provided as ''part of'' an 'instance', such as an

Amazon EC2 Amazon Elastic Compute Cloud (EC2) is a part of Amazon.com's cloud-computing platform, Amazon Web Services (AWS), that allows users to rent virtual computers on which to run their own computer applications. EC2 encourages scalable deployment of ...

(elastic compute cloud) service. As EC2 instances are primarily provided as compute resources, rather than storage resources, their storage is less robust. Their contents will be lost if the cloud instance is stopped. As these stores are part of the instance's virtual server they offer higher performance and bandwidth to the instance. They are best used for temporary storage such as caching or temporary files, with persistent storage held on a different type of server. At one time, block-level storage was provided by

storage area network A storage area network (SAN) or storage network is a computer network which provides access to consolidated, block-level data storage. SANs are primarily used to access data storage devices, such as disk arrays and tape libraries from ser ...

s (SAN) and NAS provided file-level storage. With the shift from on-premises hosting to cloud services, this distinction has shifted. Even block-storage is now seen as distinct servers (thus NAS), rather than the previous array of bare discs.

References

{{Storage virtualization Cloud storage Computer storage technologies

See also

References