Cloud Data Management Interface (CDMI) draft released

Have you developed “Cloud API fatigue” from seeing too many IaaS “Cloud APIs” lately? Are you starting to wonder how many different ways there can possibly be to launch a virtual machine via an HTTP POST? Are you wondering why everybody else seems to equate Cloud computing with on-demand server instances?

If yes, then CDMI will come as a breath of fresh air. This specification (just a draft at this point) is a rare example of a different beast. Coming out of SNIA, it endeavors to standardize the way storage resources are managed and accessed in a Cloud environment. They call this DaaS (Data storage as a Service).

The specification has two components (which may benefit from being separated in two specifications at some point). One (called “control paths”) is an interface to manage a data storage service. That interface is expected to work across many forms of data storage from block storage (like AWS EBS) to filesystems (e.g. NFS) to object stores with a CRUD interface (similar to the WebDAV volumes of the Sun API). It also mentions a “simple table space storage” storage form, but that part is pretty fuzzy.

The second component of CDMI (called “data paths”) only applies to the CRUD object store and it describes a RESTful interface for accessing it. This figure from the specification does a good job of illustrating the two different APIs in the specification (and the different types of storage envisioned).

One of the most interesting sections in the document describes the way in which the authors envision the ability to export the storage resources provisioned/managed through CDMI to other Cloud APIs. They illustrate it in an example involving OCCI (see also this joint white paper). This is very interesting and another sign that we need a shared RESTful resource control framework for Cloud computing as a first layer of standardization. One of the reasons I used to justify this claim two weeks ago was that “there will not be one API that provides control of [all the different forms of Cloud Computing], but they can share a base protocol that will make life a lot easier for developers. These Clouds won’t be isolated, developers will use them as a continuum.” One week later, this draft specification illustrates the point very well.

[As a somewhat related side note, this interesting post about what it takes to provide a large-scale resilient data service (the Google App Engine data store). And more about the Google File System in general.]