Though experts sometimes disagree on a single (or simple) definition of what a storage cloud consists of, what is definable are the requirements of cloud storage: the criteria defining both private cloud and public cloud offerings. Whether you're evaluating solutions or building your own, it's important to be aware of cloud requirements, not only to avoid cloud washing, but so your organization knows the exact benefits and drawbacks of cloud storage.
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Below is our list of nine key cloud storage criteria -- the essential elements we've determined define a true cloud storage offering. Gathered from Storage Decisions presentations by industry experts Marc Staimer, Arun Taneja and Howard Marks, our list includes some obvious criteria (Internet accessibility) as well as some advanced technological features, including object storage and multi-tenancy.
Cloud requirement 1: Massive scalability and elasticity
Whether you have 4 TB or 10 TB of storage to start, and another 3 GB or 4 TB to add the next month, the cloud storage solution you're using should be able to scale to accommodate those amounts. The same applies in scaling down; if your storage needs decrease, so should the size of your cloud. This feature, often called elasticity, allows users to pay for less storage when their data requirements shrink.
Cloud requirement 2: Object storage
Object storage uses unique identifiers instead of physical addresses to access data. Based on the name and unique ID, a storage system reads the metadata and object ID, meaning there’s no need for a single global namespace, cache coherency or high-speed networks. With an object ID replacing a file name, more extensive data than the simple "created," "modified" or "saved on" fields available in traditional file systems can accompany an object. Thus, detailed policies can be applied to objects for more efficient and automated management. Object storage has unlimited scalability, is less reliant on processing and high-speed networks, and is a fundamental building block of public and private cloud storage.
Cloud requirement 3: Allocation on-demand
When you talk about allocation on-demand, there are three things to consider: performance, capacity and objects. Another one of our cloud storage requirements, allocation on-demand is policy based; a good example of it can be found in a busy website running a one-time promotion. With cloud storage, you should be able to allocate more capacity and objects, and be able to do that just once using a policy-based, user-transparent system. Alternately, your policy could be set to allocate storage once latency reaches a certain point or throughput drops.
Cloud requirement 4: Application agnostic
Cloud storage should support all types of applications or platforms across the board, regardless of their type or interface.
Cloud requirement 5: Secure multi-tenancy
While a public cloud is shared by multiple customers, a company's data should only be visible to, or accessed by, those who own it. This can be ensured in a number of ways, primarily through encryption, and confirming that only the customer holds the encryption key for that data set.
Cloud requirement 6: Billed or licensed per usage
By definition, cloud storage is a pay-as-you-go service. Cloud storage pricing lets customers be billed for the exact number of transactions and specific amount of storage they used that month. This differs from an internally operated system in that if a company owns a 10 TB storage system, but is only storing 6 TB of data, they're still paying to maintain all 10 TB, whereas cloud users aren't.
Cloud requirement 7: Primary access via representational state transfer (REST) or Simple Object Access Protocol (SOAP)
Data stored in the cloud is accessed using REST and SOAP, Internet protocols that provide interoperability among distributed applications. Cloud storage gateways have taken prominence as a "middle man-type" of solution that translates file server commands into REST protocols that can then communicate with public cloud services.
Cloud requirement 8: Location, or Geographic, Awareness
The data stored on a cloud isn't tied to a specific, physical location. Instead, data is dispersed in such a way that even if a company is physically located on the West coast, with information stored at three locations thousands of miles apart across the United States, this shouldn't affect the user. Customers are able to move and access files and objects with certain expected response times based on service-level agreements (SLAs). If one data center is down, users should still be able to access their data.
Cloud requirement 9: Accessible via Internet
This may seem like an obvious one, but one of the cloud requirements is that clients or applications must be able to access it over the Internet or an intranet.