Chapter 9

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Content Addressed Storage
Chapter 9
Section 2 : Storage Networking Technologies and Virtualization

Chapter Objectives
Upon completion of this chapter, you will be able to:
o Describe CAS, fixed content and archives, traditional storage
solutions for archive
o Describe the features and benefits of a CAS based storage
strategy
o List the physical and logical elements of CAS
o Describe the storage and retrieval process for CAS data objects
o Describe the best suited operational environments for CAS
solutions

Lesson: CAS Overview
Upon completion of this lesson, you be able to:
o Define fixed content
o Describe traditional archival solutions and its shortcoming
o Define Content Addressed Storage (CAS)
o List benefits of CAS

What are Fixed Content and Archives
Electronic Documents
•Contracts, claims, etc.
•E-mail and attachments
•Financial spread sheets
•CAD/CAM designs
•Presentations
Digital Records
•Documents
– Checks, securities trades
– Historical preservation
•Photographs
– Personal / professional
•Surveys
– Seismic, astronomic,
geographic
Digital Assets Retained For Active Reference And Value
Leverage
Historical Value
Improve
Service Levels
Generate
New Revenues
Rich Media
•Medical
– X-rays, MRIs, CTI
•Video
– News / media, movies
– Security surveillance
•Audio
– Voicemail
– Radio

Challenges of Storing Fixed Content
o Fixed content is growing at more than 90% annually
o Significant amount of newly created information falls into this category
o New regulations require retention and data protection
o Often, long-term preservation is required (years-decades)
o Simultaneous multi-user online access is preferable to offline
storage
o Need faster access to fixed content
o Need for location independent data, enabling technology
refresh and migration
o Traditional storage methods are inadequate

Traditional storage solutions for Archive
o Three categories of archival solution are:
o Online, nearline, and offline based on the means of access
o Traditional archival solution were offline
o Traditional archival process used optical disks and tapes as media for
archival
o An archive is often stored on a Write Once Read Many (WORM) device,
such as a CD-ROM

Shortcomings of Traditional Archiving Solutions
o Tape is slow, and standards are always changing
o Optical is expensive, and requires vast amounts of media
o Recovering files from tape and optical is often time consuming
o Data on tape and optical is subject to media degradation
o Both solution require sophisticated media management
CAS has emerged as an alternative to traditional
archiving solutions

What is Content Addressed Storage (CAS)
o Object-oriented, location-independent approach to data
storage
o Repository for the “Objects”
o Access mechanism to interface with repository
o Globally unique identifiers provide access to objects

Benefits of CAS
o Content authenticity
o Content integrity
o Location independence
o Single-instance storage (SiS)
o Retention enforcement
o Record-level protection and disposition
o Technology independence
o Fast record retrieval
Additional Task
Research on role of CAS in ILM
Strategy

Lesson Summary
Key points covered in this lesson:
o CAS Definition
o Challenges of Storing Fixed Content
o Shortcomings of Traditional Archiving Solutions
o Benefits of CAS

Lesson: CAS Architecture
Upon completion of this lesson, you will be able to:
o Describe CAS architecture
o Describe Physical and logical elements of CAS
o Describe data storage and retrieval process in CAS
environment
o CAS examples

Physical Elements of CAS
o Storage devices (CAS Based)
o Storage node
o Access node
o Servers (to which storage devices
get connected)
o Client
Server
Private
LAN
Storage
Nodes
Access
Nodes
CAS System
IP
API

CAS Terminology
o Application Programming Interface (API)
o A set of function calls that enables communication
between applications or between an application and
an operating system
o BLOB (Binary Large Object)
o The actual data without the descriptive information
(metadata)
o The Distinct Bit Sequence (DBS) of user data
represents the actual content of a file and is
independent of the filename and physical location
API

CAS Terminology (Cont)
o C-Clip
o A package containing the user's data and associated
metadata
o C-Clip ID (C-Clip handle or C-Clip reference) is the CA that
the system returns to the client application
o Content Address (CA)
o An identifier that uniquely addresses the content of a file
and not its location. Unlike location-based addresses,
content addresses are inherently stable and, once
calculated, they never change and always refer to the same
content
o C-Clip Descriptor File (CDF)
o The additional XML file that the system creates when
making a C-Clip. This file includes the content addresses for
all referenced BLOBs and associated metadata

API
How CAS Stores a Data Object
Unique Content
Address is calculated
Client presents data
to API to be archived CAS System
Client
Application Server
CDF
C-Clip
(Object)
Object is sent
to CAS System via
CAS API over IP

API
How CAS Stores a Data Object
Unique Content
Address is calculated
Client presents data
to API to be archived CAS System
Client
Application Server Object is sent
to CAS System via
CAS API over IP Object
CAS System validates
the Content Address
and stores the object
Acknowledgement
returned to
application
Clip ID is retained and
stored for future use

Application Server
Client
CAS System
Object is needed by
an application
1
CAS authenticates
the request and
delivers the object
4
Application finds
Content Address of
object to be retrieved
2 Retrieval request is
sent to the CAS System via
CAS API over IP
3
How CAS Retrieves a Data Object
API
C-Clip ID

CAS Features
o Features available with most CAS systems are:
o Integrity checking
o Data protection
o Local replication
o Remote replication
o Load balancing
o Scalability
o Self-diagnosis and repair
o Report generation and event notification
o Fault tolerance
o Through the use of redundant components and data protection schemes
o Audit trails
o Documentation of management activities, access and disposition of data

Example 1: CAS Healthcare Solution
o Each X-ray image ranges from about 15MB to over 1GB
o Patient record is stored online for a period of 60-90 days
o Beyond 90 days patient records are archived
Data Stored
on CAS
Patient Studies
Stored locally for
Short-Term Use
(60 Days)
Hospital
CAS SystemApplication
Server
API

Example 2: CAS Financial Solution
o Check image size is about 25KB
o Check imaging service provider may process 50–90 million
check images per month
o Checks are stored online for a period of 60 days
o Beyond 60 days data is archived
Bank
CAS SystemApplication Server
API

Lesson Summary
Key points covered in this lesson:
o CAS architecture
o Physical and logical elements of CAS
o CAS storage and retrieval process
o CAS solution examples

Chapter Summary
Key points covered in this chapter:
o Benefits of CAS based storage strategy
o Overview of physical and logical elements of CAS
o Storing and retrieving data from CAS
o CAS application examples

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