Day of REST approaches for the cloud
It's a style thing
The REST interface style focusses "upon the generic connector interface of resources and representations has enabled intermediate processing, caching, and substitutability of components, which in turn has allowed Web-based applications to scale from 100,000 requests/day in 1994 to 600,000,000 requests/day in 1999."
It has been said that a RESTful access has four verbs for operations and many nouns, one for each resource that can be operated upon via its URI. The verbs are GET (meaning read), POST (meaning create, amend or delete), PUT (meaning create or update) and DELETE (meaning delete of course).
Cloud storage and cloud computing are seen as being gigantic in scale, and REST proponents say that the REST web services architecture is suited to such scaling. They note that storage clouds such as SoftLayer's CloudLayer, Amazon's S3, Nirvanix' SDN and Rackspace's Cloud Files all use a RESTFul architecture.
NFS and CIFS are, simplistically, client-server file data requests whose architecture predated the web. As such they are not suited to cloud storage although legacy NFS/CIFS-using applications can interface to cloud storage through NFS/CIFS protocol access layered onto interface styles such as REST. Nirvanix offers CloudNAS for this purpose.
SOAP and REST
It offers two Web Services APIs though; SOAP and REST. SOAP stands for Simple Object Access Protocol, and was developed by Microsoft in 1998. It uses eXtensible Markup Language (XML) as its message format and various application-level protocols such as RPC (Remote Procedure Call) and HTTP to send messages to servers and get results.
SOAP can be differentiated from REST this way; to use SOAP, developers have to understand the XML spec and will generally need a SOAP toolkit. Every SOAP request and response is wrapped inside an XML coat and this, with associated namespace and data typing information, means SOAP responses can be up to ten times larger than equivalent REST messages. SOAP is therefore heavier weight than REST. SOAP, it is said, is a protocol to use with distributed computing based on XML. REST is not.
We could view REST and SOAP as complementary. SOAP is also, it appears, getting RESTful with a version of its spec admitting the use of URIs be used to expose certain services.
From the storage admin and buying point of view, SOAP and REST are upstream matters. Upstream of the storage array and starting on the server that interfaces them to the ultimate users of those arrays across the Internet cloud. For storage consuming applications that look to get and/or develop cloud storage services then SOAP and REST are highly relevant.
REST is a way of setting up and operating Web Services interactions, not a formal prescription of exactly how you develop them.
Since REST is an architectural style there is no defined REST protocol, no standard REST toolkit, and no defined and standard REST facility which says whether a particular cloud storage interface is fully RESTful or not. It is all, literally, cloudy. ®