In Part 1 about the
cloud, we explored
the “Wild West” opportunities
the cloud; opening the
horizon to what the
cloud offers to users
who are just now beginning
to understand the various value and
The appeal of the cloud for storage purposes
comes, in part, from the appearance
that the cloud can have infinite and scalable
storage. Scalability infers that the cloud provides
benefits that will allow the addition of
tens to hundreds of users for short or long
periods of time—without having to worry
about or invest in expensive hardware, software
or services upfront.
Cloud storage is fundamentally about
the delivery of virtualized storage on demand.
Hence, there is the perception that
the cloud is elastic in nature; that is, it can
handle sudden, unanticipated or extraordinary
loads. Elasticity and scalability are not
the same, and thus, the interchangeable use
of these terms should not be encouraged.
USE OF THE CLOUD
On the consumer front, the pay-as-you
go model extends the belief that the cloud
is affordable. Buy what you need, when you
need it—nothing more. Commercial services
for consumers are attracting vast new users
to the cloud. Business uses are expanding
with the concept and deployment of
“private cloud” services continuing.
Cloud services and cloud storage are
built on familiar technologies including
Service Oriented Architectures (SoA); and
among other practices, may be governed
in part by Service Level Agreements (SLAs)
As with other forms of technology, users
hope there can be uniformity in the interfaces,
capabilities and prospects associated
with the cloud. This is inherently possible
when standards are written and adhered
to. However, with any new set of services, it
can often take years before sufficient documentation,
experience and devotion to developing
those standards may occur.
Architecturally, for cloud storage services,
the resources available to users (clients) are
exposed as data paths, i.e., functional interfaces,
which are managed via control paths,
otherwise known as management interfaces.
Many of the offerings initially available
for cloud storage were of best-effort quality,
much like the delivery of data using TCP/IP.
Since then, there has been serious work
on developing methods that support a quality
of service (QoS) level, which will in turn,
lead to deployment of additional data-related
The Storage Networking Industry Association
(SNIA) has been diligently working
since before 2010 on an initiative to
develop a functional interface that applications
can use to create, retrieve, update and
delete data elements from the cloud. This
work is called the “Cloud Data Management
Interface” (CDMI), and as of June 2012, was
at Version 1.0.2.
You will hear a lot about CDMI in the
near future. The working document, its publication
and distribution is controlled by
SNIA. Full and complete credit is given to
SNIA for much of the context of the material
presented in this article.
The CDMI effort is believed by many to
be the foremost set of specifications for the
universal uses of cloud storage. It is a complex
set of specifications rooted in the fundamentals
of object-based storage. Where
possible, the interface design for the CDMI
specification uses RESTful (Representational
State Transfer) principles, which is essentially
a simpler alternative to SOAP (Simple Object Access Protocol) and WSDL (Web Services
Description Language). REST has gained
widespread acceptance across the Web as
the predominant service design model.
Fig. 1: Cloud computing—composed of cloud storage and cloud services
In CDMI for data storage operations, the
concept of objects and containers are introduced.
Container objects are analogous to
the directories in a file system. They are the
elemental grouping of stored data within
the interface. A container (as the parent)
will have zero or more child objects that
must include standardized (plus optional)
metadata, which would be specified by the
cloud user and generated by the cloud storage
Every container object will possess a
globally unique object identifier, or OID,
that never changes throughout the life of
the object. Accessing the container object
is achieved through one or more Uniform
Resource Identifier (URI) addresses.
Like almost all other sets of stored digital
data, generated metadata becomes an
essential (and required) component that,
in CDMI, is used for access control and,
from the user side, can include arbitrary
user-defined items that help in describing
the information about the data in the container—
or for other purposes deemed necessary
by the user.
Once an object is created, the storage
system metadata is generated (by the cloud
storage system), and is made available to a
CDMI client during any subsequent retrieval
of data from the cloud.
CDMI also includes three functional logging
capabilities: object logging, security
logging and data management logging. The
log messaging formats are not defined in
CDMI, although it is anticipated that future
logging standards will be addressed.
Other capabilities include summary billing
information, the export of containers as
NFS or CIFS shares, queries and persistent
first-in, first out queues, and serialization—
the capability to export data and metadata
into another cloud system.
For the present, the efforts of SNIA to
promote a standardized interface that will
allow users to enjoy the benefits of private
(restricted) clouds, public (unrestricted)
clouds and potential subsequent other offerings,
are already being implemented by the
industry. The delivery of other services (Fig.
1), including Software as a Service (SaaS),
Platforms as a Service (PaaS), Infrastructure
as a Service (Iaas) and Data Storage as a Service
(DaaS) are surely in our future.
Whether you see your applications as
public (open) or private (constrained within
the bounds of your business), the “cloud”
is here and is accepted. Building the future
of your enterprise will involve the cloud as
service or storage needs grow.
CDMI is a registered trademark of SNIA;
complete details on the current CDMI
specification can be found at http://cdmi.
Karl Paulsen (CPBE) is a SMPTE Fellow
and chief technologist at Diversified
Systems. Read more about these and other
storage topics in his book “Moving Media
Storage Technologies.” Contact Karl at