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n the life cycle of information, data is actively
created, accessed, edited, and changed. As
Fixed Content and Archives
data ages, it becomes less likely to change
and eventually becomes “fixed” but continues to
Single-Instance Storage
be accessed by multiple applications and users.
Object Storage and Retrieval
This data is called fixed content.
Traditionally, fixed content was not treated as
Content Authenticity
a specialized form of data and was stored using
a variety of storage media, ranging from optical
disks to tapes to magnetic disks. While these traditional technologies store
content, none of them provide all of the unique requirements for storing and
accessing fixed content.
Accumulations of fixed content such as documents, e-mail messages, web pages,
and digital media throughout an organization have resulted in an unprecedented
growth in the amount of data. It has also introduced the challenge of managing
fixed content. Furthermore, users demand assurance that stored content has not
changed and require an immediate online access to fixed content. These requirements resulted in the development of Content-Addressed Storage (CAS).
CAS is an object-based system that has been purposely built for storing fixed
content data. It is designed for secure online storage and retrieval of fixed content. Unlike file-level and block-level data access that use file names and the
physical location of data for storage and retrieval, CAS stores user data and its
attributes as separate objects. The stored object is assigned a globally unique
address known as a content address (CA). This address is derived from the object’s
binary representation. CAS provides an optimized and centrally managed storage solution that can support single-instance storage (SiS) to eliminate multiple
copies of the same data.
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This chapter describes fixed content and archives, traditional solutions
deployed for archives and their limitations, the features and benefits of CAS,
CAS architecture, storage and retrieval in a CAS environment, and examples
of CAS solutions.
9.1 Fixed Content and Archives
Data is accessed and modified at varying frequencies between the time it is created and discarded. Some data frequently changes, for example, data accessed
by an Online Transaction Processing (OLTP) application. Some data that does
not typically change, but is allowed to change if required is, for example, bill
of material and design documents.
Another category of data is fixed content, which defines data that cannot be
changed. X-rays and pictures are examples of fixed content data. It is mandatary
for all organizations to retain some data for an extended period of time due to
government regulations and legal/contractual obligations. Fixed data, which
is retained for future reference or business value, is referred to as fixed content
asset. Some examples of fixed content asset include electronic documents, e-mail
messages, Web pages, and digital media (see Figure 9-1).
Organizations make use of these digital assets to generate new revenues,
improve service levels, and leverage historical value. This demands frequent
and quick retrieval of the fixed contents at multiple locations. An archive is a
repository where fixed content is placed. Online data availability in the archive
can further increase the business value of the referenced information.
New Revenues
Service Levels
Historical Value
Digital Assets Retained for Active Reference and Value
Electronic Documents
Digital Records
Rich Media
• Documents
— Checks and securities
— Historical preservation
• Photographs
— Personal/professional
• Surveys
— Seismic, astronomic,
• Medical
— X-rays, MRIs, CT scan
• Video
— News/media, movies
— Security surveillance
• Audio
— Voice mail
— Radio
Contracts, claims, etc.
E-mail attachments
Financial spreadsheets
CAD/CAM designs
Figure 9-1: Examples of fixed content data
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9.2 Types of Archives
An electronic data archive is a repository for data that has fewer access
requirements. It can be implemented as online, nearline, or offline based on
the means of access:
Online archive: The storage device is directly connected to the host
to make the data immediately available. This is best suited for active
Nearline archive: The storage device is connected to the host and information is local, but the device must be mounted or loaded to access
the information.
Offline archive: The storage device is not directly connected, mounted,
or loaded. Manual intervention is required to provide this service before
information can be accessed.
An archive is often stored on a write once read many (WORM) device, such
as a CD-ROM. These devices protect the original file from being overwritten. Some tape devices also provide this functionality by implementing filelocking capabilities in the hardware or software. Although these devices
are inexpensive, they involve operational, management, and maintenance
Requirements to retain archives have caused corporate archives to grow at
a rate of 50 percent or more per year. At the same time, organizations must
reduce costs while maintaining required service-level agreements (SLAs).
Therefore, it is essential to find a solution that minimizes the fixed costs of
the archive’s operations and management.
Archives implemented using tape devices and optical disks involve many
hidden costs. The traditional archival process using optical disks and tapes is
not optimized to recognize the content, so the same content could be archived
several times. Additional costs are involved in offsite storage of media and
media management. Tapes and optical media are also susceptible to wear
and tear. Frequent changes in these device technologies lead to the overhead
of converting the media into new formats to enable access and retrieval.
Government agencies and industry regulators are establishing new laws
and regulations to enforce the protection of archives from unauthorized
destruction and modification. These regulations and standards affect all businesses and have established new requirements for preserving the integrity
of information in the archives. These requirements have exposed the hidden
costs and shortcomings of the traditional tape and optical media archive
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Businesses such as banking, finance, and health care have to
comply with standards enforced by regulators for archived
data. These rules detail the regulatory requirements for
maintaining the authenticity, integrity, and availability of all
business records, contracts, legal documents, and business
communications in electronic data formats. These regulations may also state that all businesses are required to inform their customers
when their electronic data is compromised.
SEC Rule 17a-3 and 17a-4 of the Securities Exchange Act of 1934, the
Sarbanes-Oxley Act, and the Health Insurance Portability and Accountability
Act (HIPAA) are some examples of these regulations.
9.3 Features and Benefits of CAS
CAS has emerged as an alternative to tape and optical solutions because it overcomes many of their obvious deficiencies. CAS also meets the demand to improve
data accessibility and to properly protect, dispose of, and ensure service-level agreements for archived data. The features and benefits of CAS include the following:
Content authenticity: It assures the genuineness of stored content. This
is achieved by generating a unique content address and automating the
process of continuously checking and recalculating the content address
for stored objects. Content authenticity is assured because the address
assigned to each piece of fixed content is as unique as a fingerprint. Every
time an object is read, CAS uses a hashing algorithm to recalculate the
object’s content address as a validation step and compares the result to
its original content address. If the object fails validation, it is rebuilt from
its mirrored copy.
Content integrity: Refers to the assurance that the stored content has
not been altered. Use of hashing algorithm for content authenticity also
ensures content integrity in CAS. If the fixed content is altered, CAS
assigns a new address to the altered content, rather than overwrite the
original fixed content, providing an audit trail and maintaining the fixed
content in its original state. As an integral part of maintaining data integrity and audit trail capabilities, CAS supports parity RAID protection
in addition to mirroring. Every object in a CAS system is systematically
checked in the background. Over time, every object is tested, guaranteeing content integrity even in the case of hardware failure, random error,
or attempts to alter the content with malicious intent.
Location independence: CAS uses a unique identifier that applications
can leverage to retrieve data rather than a centralized directory, path
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names, or URLs. Using a content address to access fixed content makes
the physical location of the data irrelevant to the application requesting the data. Therefore the location from which the data is accessed is
transparent to the application. This yields complete content mobility to
applications across locations.
Single-instance storage (SiS): The unique signature is used to guarantee
the storage of only a single instance of an object. This signature is derived
from the binary representation of the object. At write time, the CAS system
is polled to see if it already has an object with the same signature. If the
object is already on the system, it is not stored, rather only a pointer to
that object is created. SiS simplifies storage resource management tasks,
especially when handling hundreds of terabytes of fixed content.
Retention enforcement: Protecting and retaining data objects is a core
requirement of an archive system. CAS creates two immutable components: a data object and a meta-object for every object stored. The metaobject stores object’s attributes and data handling policies. For systems that
support object-retention capabilities, the retention policies are enforced
until the policies expire.
Record-level protection and disposition: All fixed content is stored in
CAS once and is backed up with a protection scheme. The array is composed of one or more storage clusters. Some CAS architectures provide an
extra level of protection by replicating the content onto arrays located at
a different location. The disposition of records also follows the stringent
guidelines established by regulators for shredding and disposing of data
in electronic formats.
Technology independence: The CAS system interface is impervious to
technology changes. As long as the application server is able to map the
original content address the data remains accessible. Although hardware
changes are inevitable, the goal of CAS hardware vendors is to ensure
compatibility across platforms.
Fast record retrieval: CAS maintains all content on disks that provide
subsecond “time to first byte” (200 ms–400 ms) in a single cluster. Random
disk access in CAS enables fast record retrieval.
9.4 CAS Architecture
The CAS architecture is shown in Figure 9-2. A client accesses the CAS-Based
storage over a LAN through the server that runs the CAS API (application
programming interface). The CAS API is responsible for performing functions
that enable an application to store and retrieve the data.
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CAS architecture is a Redundant Array of Independent Nodes (RAIN). It contains
storage nodes and access nodes networked as a cluster by using a private LAN
that is internal to it. The internal LAN can be reconfigured automatically to
detect the configuration changes such as the addition of storage or access nodes.
Clients access the CAS on a separate LAN, which is used for interconnecting
clients and servers to the CAS.
The nodes are configured with low-cost, high-capacity ATA HDDs. These
nodes run an operating system with special software that implements the features and functionality required in a CAS system.
CAS System
Figure 9-2: CAS Architecture
When the cluster is installed, the nodes are configured with a “role” defining the functionality they provide to the cluster. A node can be configured as
a storage node, an access node, or a dual-role node. Storage nodes store and protect data objects. They are sometimes referred to as back-end nodes. Access nodes
provide connectivity to application servers through the customer’s LAN. They
establish connectivity through a private LAN to the storage nodes in the cluster. The number of access nodes is determined by the amount of user required
throughput from the cluster. If a node is configured solely as an “access node,”
its disk space cannot be used to store data objects. This configuration is generally found in older installations of CAS. Storage and retrieval requests are sent
to the access node via the customer’s LAN. Dual-role nodes provide both storage
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and access node capabilities. This node configuration is more typical than a
pure access node configuration.
Almost all CAS products have the same features and options. Some may be
implemented differently, but the following features are an essential part of any
CAS solution:
Integrity checking: It ensures that the content of the file matches the digital
signature (hashed output or CA). The integrity checks can be done on every
read or by using a background process. If problems are identified in any
of the objects the nodes automatically repair or regenerate the object.
Data protection and node resilience: This ensures that the content stored
on the CAS system is available in the event of disk or node failure. Some
CAS systems provide local replication or mirrors that copy a data object to
another node in the same cluster. This decreases the total available capacity by 50 percent. Parity protection is another way to protect CAS data.
It uses less capacity to store data, but takes longer to regenerate the data
if corrupted. Remote replication copies data objects to a secondary storage device in a remote location. Remote replication is used as a disasterrecovery solution or for backup. Replication technologies are detailed in
Chapters 13 and 14.
Load balancing: Distributes data objects on multiple nodes to provide
maximum throughput, availability, and capacity utilization.
Scalability: Adding more nodes to the cluster without any interruption
to data access and with minimum administrative overhead.
Self diagnosis and repair: Automatically detects and repairs corrupted
objects and alert the administrator of any potential problem. These failures
can be at an object level or a node level. They are transparent to the users
who access the archive. CAS systems can be configured to alert remote
support teams who diagnose and make repairs remotely.
Report generation and event notification: Provides on-demand reporting and event notification. A command-line interface (CLI) or a graphical user interface (GUI) can produce various types of reports. Any event
notification can be communicated to the administrator through syslog,
SNMP, SMTP, or e-mail.
Fault tolerance: Ensures data availability if a component of the CAS system fails, through the use of redundant components and data protection
schemes. If remote replication of CAS is implemented, failover to the remote
CAS system occurs when the primary CAS system is unavailable.
Audit trails: Enable documentation of management activity and any
access and disposition of data. Audit trails are mandated by compliance
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9.5 Object Storage and Retrieval in CAS
The process of storing and retrieving objects in CAS is explained in Figures 9-3
and 9-4, respectively. This process requires an understanding of the following
CAS terminologies:
Application programming interface (API): A high-level implementation
of an interface that specifies the details of how clients can make service
requests. The CAS API resides on the application server and is responsible
for storing and retrieving the objects in a CAS system.
Access profile: Used by access applications to authenticate to a CAS
cluster and by CAS clusters to authenticate themselves to each other for
Virtual pools: Enable a single logical cluster to be broken up into multiple
logical groupings of data.
Binary large object (BLOB): The actual data without the descriptive
information (metadata). The distinct bit sequence of user data represents the actual content of a file and is independent of the name and
physical location.
Content address (CA): An object’s address, which is created by a hash
algorithm run across the binary representation of the object. While generating a CA, the hash algorithm considers all aspects of the content,
returning a unique content address to the user’s application.
A unique number is calculated from the sequence of bits that constitutes
file content. If even a single character changes in the file, the resulting
CA is different. A hash output, also called a digest, is a type of fingerprint
for a variable-length data file. This output represents the file contents
and is used to locate the file in a CAS system. The digest can be used to
verify whether the data is authentic or has changed because of equipment failure or human intervention. When a user tries to retrieve or open
a file, the server sends the CA to the CAS system with the appropriate
function to read the file. The CAS system uses the CA to locate the file
and passes it back to the application server.
C-Clip: A virtual package that contains data (BLOB) and its associated
CDF. The C-Clip ID is the CA that the system returns to the client application. It is also referred as a C-Clip handle or C-Clip reference.
C-Clip Descriptor File (CDF): An XML file that the system creates while
making a C-Clip. This file includes CAs for all referenced BLOBs and
associated metadata. Metadata includes characteristics of CAS objects
such as size, format, and expiration date.
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Referring to Figure 9-3, the data object storage process in a CAS system is
as follows:
1. End users present the data to be archived to the CAS API via an application. The application server may also interact directly with the source (e.g.,
an X-ray machine) that generated this fixed content.
2. The API separates the actual data (BLOB) from the metadata and the CA
is calculated from the object’s binary representation.
3. The content address and metadata of the object are then inserted into the
C-Clip Descriptor File (CDF). The C-clip is then transferred to and stored
on the CAS system.
4. The CAS system recalculates the object’s CA as a validation step and stores
the object. This is to ensure that the content of the object has not changed.
5. An acknowledgment is sent to the API after a mirrored copy of the CDF
and a protected copy of the BLOB have been safely stored in the CAS
system. After a data object is stored in the CAS system, the API is given
a C-Clip ID and C-Clip ID is stored local to the application server.
6. Using the C-Clip ID, the application can read the data back from the CAS
Once an object is stored successfully, it is made available to end users
for retrieval and use. The content address is usually hidden from the
user. A user accesses the file stored on CAS by the same file name. It is
the application server that references the CA to retrieve the stored content; this process is transparent to the user. No modification is needed
to the application’s user interface to accommodate the CAS storage and
retrieval process.
Application Server
CAS System
X-ray object
Figure 9-3: Storing data objects on CAS
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The process of data retrieval from CAS follows these steps:
1. The end user or an application requests an object.
2. The application queries the local table of C-Clip IDs stored in the local
storage and locates the C-Clip ID for the requested object.
3. Using the API, a retrieval request is sent along with the C-Clip ID to the
CAS system.
4. The CAS system delivers the requested information to the application,
which in turn delivers it to the end user.
Application Server
CAS System
Figure 9-4: Data object retrieval from CAS system
9.6 CAS Examples
Organizations have deployed CAS solutions to solve several business problems.
Two solutions are described in detail in the following sections.
9.6.1 Health Care Solution: Storing Patient Studies
A large health care center examines hundreds of patients every day and generates
large volumes of medical records. Each record may be composed of one or more
images that range in size from about 15 MB for standard digital X-ray images to
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over 1 GB for oncology studies. The patient records are stored online for a period
of 60–90 days for immediate use by attending physicians. Even if a patient’s
record is no longer needed for any reason, HIPAA requirements stipulate that
the records should be kept in the original formats for at least seven years.
Beyond 90 days, hospitals may backup images to tape or send them to an
offsite archive service for long-term retention. The cost of restoring or retrieving an image in long-term storage may be five to ten times more than leaving
the image online. Long-term storage may also involve extended recovery time,
ranging from hours to days. Medical image solution providers offer hospitals
the capability to view medical records, such as online X-ray images, with sufficient response times and resolution to enable rapid assessments of patients.
Figure 9-5 illustrates the use of CAS in this scenario. The patient records are
moved to the CAS system after 60-90 days. This facilitates long-term storage and
at the same time when immediate access is needed, the records are available by
accessing the CAS system.
Patient Studies
Data Stored
on CAS
Stored locally for
Short-Term Use
(60 Days)
CAS System
Figure 9-5: Storing patient studies on CAS system
9.6.2 Finance Solution: Storing Financial Records
In a typical banking scenario, images of checks, each about 25 KB in size,
are created and sent to archive services over an IP network. A check imaging service provider may process 50–90 million check images per month.
Typically, check images are actively processed in transactional systems for
about five days.
For the next 60 days, check images may be requested by banks or individual consumers for verification purposes at the rate of about 0.5 percent
of the total check pool, or about 250,000–450,000 requests. Beyond 60 days,
access requirements drop drastically, to as few as one for every 10,000 checks.
Figure 9-6 illustrates the use of CAS in this scenario. The check images are
stored on a CAS system, starting at day 60 and can be held there indefinitely.
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A typical check image archive can approach a size of 100 TB. Check imaging is
one example of a financial service application that is best serviced with CAS.
Customer transactions initiated by e-mail, contracts, and security transaction
records may need to be kept online for 30 years; CAS is the preferred storage
solution in such cases.
Application Server
CAS System
Figure 9-6: Storing finiancial records on CAS system
Business organizations need to move data between storage
tiers for many reasons, including cost, protection, and compliance, depending on its value over time. HSM is a policybased management system of file backup and archiving. The
policies are established to store data on different tiers of
storage based on the relevance and importance of the information. An example of a policy is if a file on a high-performance storage tier
is not accessed for 120 days, it should be migrated to a low performance storage tier or archived on the CAS system. At the same time, when users need
that migrated file, access to it must be provided seamlessly. HSM implements
such policies and automates the process of migration and recall of data from
different tiers of storage. The process of migration is completely transparent
to the user. After the migration, the original file on the high-performance storage is replaced with a stub file, which acts as a placeholder and looks like the
original file to the user.
9.7 Concepts in Practice: EMC Centera
EMC Centera is a simple, affordable, and secure repository for information
archiving. EMC Centera is the first platform designed and optimized specifically
to deal with the storage and retrieval of fixed content, meeting performance,
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Content-Addressed Storage
compliance, and regulatory requirements. Compared to traditional archive solutions, EMC Centera provides faster record retrieval, SiS, guaranteed content
authenticity, self-healing, and support for numerous industry regulatory standards. Visit for the latest information.
9.7.1 EMC Centera Models
EMC Centera is offered in three different models to meet different types of user
requirements—EMC Centera Basic, EMC Centera Governance Edition, and EMC
Centera Compliance Edition Plus (CE+):
EMC Centera Basic: Provides all functionality without the enforcement
of retention periods.
EMC Centera Governance Edition: Provides the retention capabilities
required by organizations to responsibly manage electronic records in
addition to the features provided by EMC Centera Basic. Deploying
Governance Edition enforces organizational and application policies for
information retention and disposition.
CE+: Provides extensive compliance capabilities. CE+ is designed to meet
the requirements of the most stringent of regulated business environments for electronic storage media as established by regulations from
the Securities and Exchange Commission (SEC), or other national and
international regulatory groups.
9.7.2 EMC Centera Architecture
The architecture of the RAIN-based EMC Centera system is designed to be
highly scalable and to store petabytes of content. While the EMC Centera cabinet
can accommodate 32 nodes, the entry level configuration starts with as few as 4
nodes and 2 internal switches and is expandable in increments of 4 nodes. The
nodes run a Linux operating system and CentraStar software to implement all
the CAS functionality. A collection of nodes and internal switches is referred to
as a cube. A cube contains two internal switches and a maximum of 16 nodes.
A fully configured cabinet is comprised of two cubes, as shown in Figure 9-7.
The EMC Centera node contains four SATA HDDs and a dual-source power
supply that enables EMC Centera nodes to connect to two power sources. Each
power outlet on a node connects to a separate power rail.
Figure 9-8 illustrates the EMC Centera architecture. Each node contains more
than 1 TB of usable capacity and can be configured as access and/or storage
nodes. EMC Centera has two 24-port 2 gigabit internal switches that provide
communications for up to 16 nodes within the private LAN. Several cabinets
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Storage Networking Technologies and Virtualization
of these nodes and switches can be connected to form an EMC Centera cluster.
An EMC Centera domain consists of one or more clusters. Applications may
support multiple clusters within a EMC Centera domain. Each cabinet can host
up to 23 TB. The usable protected capacity varies depending on whether it uses
content protection parity (CPP) or content protection mirrored (CPM).
In CPP, the data is fragmented into segments, with an additional parity segment.
Each segment is on a different node, similar to a file-type RAID. If a node or a disk
fails, the other nodes regenerate the missing segment on a different node.
In CPM, each data object is mirrored and each mirror resides on a different
node (refer to Figure 9-8). If a node or a disk fails, the EMC Centera software
automatically broadcasts to the node with the mirrored copy to regenerate
another copy to a different node so that two copies are always available.
Power Supply
Processor Card Cooling Tunnel
1 Cube = 16 nodes + 2 internal switches
1 Cabinet = 2 Cubes
EMC Centera
Figure 9-7: EMC Centera configuration
Both CPP and CPM provide total protection against failure using EMC Centera’s
unique self-healing functions. With the self-healing feature, if any component in the
node or the entire node fails, data is regenerated to a different part of the cluster,
ensuring that data is always protected. In addition to this “organic regeneration” process, there are other processes that run continuously in the background,
verifying objects by scrubbing and ensuring that objects are not corrupted. The
self-managing and configuring functionality enable rapid installation and implementation of EMC Centera.
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Content-Addressed Storage
EMC Centera protects users from technology changes by allowing various
generations to coexist in a single CAS cluster.
Mirrored Content
To Server
1 2 3 4 5 6
Power Rails
Figure 9-8: EMC Centera architecture
9.7.3 Centera Tools
A group of tools are available to users and service personnel to manage the
functions of EMC Centera. They include EMC Centera Viewer, EMC Centera
Monitor, EMC Centera Console, and EMC Centera Health Reporting:
EMC Centera Viewer: It is a GUI that is loaded to a client that has network
access to EMC Centera. The tool provides a simple means of displaying
EMC Centera’s capacity utilization and operational performance. It also
enables the system administrator to change any site-specific information,
such as the public network information and end-user contact information.
EMC Centera Viewer is commonly used by service personnel to perform
maintenance and to upgrade the CentraStar code.
EMC Centera Monitor: It is a tool that enables users to monitor a single
cube in EMC Centera, by displaying system properties such as configuration, capacity, and software version.
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EMC Centera Console: It is a web-based management tool that enables
system operators to view detailed information about alerts, configurations,
performance, and relationships between multiple EMC Centera clusters.
EMC Centera Health Reporting: It is done through an automatic e-mail message that an EMC Centera cluster periodically sends to the EMC Customer
Support Center or a list of predefined recipients. The message reports the
current status of the EMC Centera cluster. This enables remote monitoring,
diagnosis, and support for EMC Centera hardware and software.
9.7.4 EMC Centera Universal Access
An important feature of EMC Centera, when compared to traditional archive
solutions, is that the EMC Centera archive is online. In addition, the EMC
Centera archive is accessible from any application or platform. EMC Centera
Universal Access acts as a high-performance store and forward protocol translator. It communicates with application servers using network file protocols
(NFS, CIFS, HTTP) and with an EMC Centera cluster through Centera API (see
Figure 9-9).
Servers With EMC Centera
API Integrated Application
with EMC
EMC Centera
Servers Without EMC Centera
API Integrated Application
Figure 9-9: EMC Centera Universal Access
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Content-Addressed Storage
With EMC Centera Universal Access, any enterprise application that can
mount a network drive or use FTP and HTTP can take advantage of EMC
Centera’s benefits. From home-grown applications to nonintegrated versions of
applications, EMC Centera Universal Access makes it possible to utilize EMC
Centera in customer environments with no change to existing applications. This
greatly simplifies and accelerates deployment.
Understanding the information lifecycle enables storage designers to adopt
different storage technology to meet data archival requirements. CAS offers
a centrally managed networked storage solution for fixed content. CAS has
enabled IT organizations to realize significant cost savings and improve operational efficiency and data protection. CAS meets stringent regulatory requirements that have helped organizations avoid penalties and issues associated with
regulatory noncompliance. CAS eliminates data duplication with SiS, which
reduces IT maintenance costs and increases long-term return on investment
for storage systems.
This chapter outlined the challenges involved in managing fixed content,
the CAS architecture and its benefits, and how CAS is deployed and managed,
using EMC Centera as an example.
Storage networking technologies have provided the primary architecture that
has evolved and matured to meet the business’s information storage demands.
As this evolution continues, organizations have started using multi-vendor and
multi-generation technologies that must work together without compromising
business requirements. The virtualization technologies described in the next
chapter provides more flexibility and scalability to meet next-generation storage needs.
1. Explain how a CAS solution fits into the ILM strategy.
2. To access data in a SAN, a host uses a physical address known as a logical
block address (LBA). A host using a CAS device does not use (or need) a
physical address. Why?
3. The IT department of a department store uses tape to archive data.
Explain 4–5 major points you could provide to persuade the IT department to move to a CAS solution. How would your suggestions impact the
IT department?