(06CS833) UNIT-1 STORAGE AREA NETWOKS - VTU notes · (06CS833) UNIT-1 STORAGE AREA NETWOKS ....
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UNIT 1
INTRODUCTION
INTRODUCTION: Server Centric IT Architecture and its Limitations; Storage – Centric IT Architecture and its advantages. Case study: Replacing a server with Storage Networks; The Data Storage and Data Access problem; The Battle for size and access.
SERVER-CENTRIC IT ARCHITECTURE AND ITS LIMITATIONS
With a neat diagram, explain the server centric IT architecture and bring out its limitations.
(JUNE 2012, JUNE/JULY 2011) (10marks) In conventional IT architectures, storage devices are normally only connected to a single server. To increase fault-
tolerance, storage devices are sometimes connected to two servers, with only one server actually able to use the
storage device at any one time.
In both cases, the storage device exists only in relation to the server to which it is connected. Other servers cannot
directly access the data; they always have to go through the server that is connected to the storage device. This
conventional IT architecture is therefore called server-centric IT architecture. In this approach, servers and storage
devices are generally connected together by SCSI cables.
In conventional server-centric IT architecture storage devices exist only in relation to the one or two servers to
which they are connected. The failure of both of these computers would make it impossible to access this data. Most
companies find this unacceptable. At least some of the company data (for example, patient files, and websites) must be
available around the clock.
Figure 1.1 In a server-centric IT architecture storage devices
exist only in relation to servers
Figure 1.2 The storage capacity on server 2 is full. It cannot make use of storage space free on server 1 and server 3
is still storage space free on server 1 and server 3
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Although the storage density of hard disks and tapes is increasing all the time due to ongoing technical
development, the need for installed storage is increasing even faster. It is necessary to connect ever more storage
devices to a computer. But each computer can accommodate only a limited number of I/O cards (for example, SCSI
cards). Furthermore, the length of SCSI cables is limited to a maximum of 25 m. This means that the storage capacity
that can be connected to a computer using conventional technologies is limited.
In server-centric IT environments the storage device is statically assigned to the computer to which it is connected.
In general, a computer cannot access storage devices that are connected to a different computer. This means that if a
computer requires more storage space than is connected to it, it cannot still use the free space present in another
computer.
Storage devices are often scattered throughout an entire building or branch. Computers may be consciously set up
where the user accesses the data in order to reduce LAN data traffic. The result is that the storage devices are
distributed throughout many rooms, which are neither protected against unauthorized access nor sufficiently air-
conditioned.
Paragraphs 3,4,5,6 contain the limitations.
STORAGE-CENTRIC IT ARCHITECTURE AND ITS ADVANTAGES
Explain with a neat diagram, the working and advantages of storage centric IT architecture.
(JUNE 2012) (10marks)
Storage networks can solve the problems of server-centric IT architecture. Storage networks open up new
possibilities for data management.
The idea behind storage networks is that the SCSI cable is replaced by a network that is installed in addition to the
existing LAN and is primarily used for data exchange between computers and storage devices.
In contrast to server-centric IT architecture, in storage networks storage devices exist completely independently of
any computer. Several servers can access the same storage device directly over the storage network without another
server having to be involved.
Storage devices are thus placed at the centre of the IT architecture. IT architectures with storage networks are
therefore known as storage-centric IT architectures.
When a storage network is introduced, the storage devices are usually also consolidated. This involves replacing the
many small hard disks attached to the computers with a large disk subsystem.
Disk subsystems currently have a maximum storage capacity of several ten terabytes. The storage network permits
all computers to access the disk subsystem and share it.
Free storage capacity can thus be flexibly assigned to the computer that needs it at the time. In the same manner,
many small tape libraries can be replaced by one big one.
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More and more companies are converting their IT systems to a storage-centric IT architecture. It has now become a
permanent component of large data centers and the IT systems of large companies. More and more medium-sized
companies and public institutions are now considering storage networks.
Depending upon the source, it is predicted that by the end of 2004 two-thirds of external storage capacity will be
connected by means of storage networks.
CASE STUDY: REPLACING A SERVER WITH STORAGE NETWORKS
Explain with a neat diagram, the replacing of a server with Storage Networks (8-10marks) In a production environment an application server is no longer powerful enough. The ageing computer must be
replaced by a higher-performance device. The procedure is complicated in a conventional, server-centric IT
architecture; it can be carried out very elegantly in a storage network.
Before the exchange, the old computer is connected to a storage device via the storage network, which it uses
partially (Figure 1.4 shows stages 1, 2 and 3).
First, the necessary application software is installed on the new computer. The new computer is then set up at
the location at which it will ultimately stand. With storage networks it is possible to set up the computer and
storage device several kilometers apart.
Next, the production data for generating test data within the disk subsystem is copied. Modern storage systems
can (practically) copy even terabyte-sized data files within seconds. This function is called instant copy.
Then the copied data is assigned to the new computer and the new computer is tested intensively.
After successful testing, both computers are shut down and the production data assigned to the new server.
The assignment of the production data to the new server also takes just a few seconds.
Figure 1.3 In storage-centric IT architecture the SCSI cables are replaced by a network. Storage devices now exist independently of a server
is still storage space free on server 1 and server 3
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Finally, the new server is restarted with the production data.
THE DATA STORAGE AND DATA ACCESS PROBLEM
THE CHALLENGE OF DESIGNING APPLICATIONS
Storing and accessing data depends on the business application.
Recognizing the function of application design in today’s component driven world is a challenging task, these
functions are necessary to facilitate user data within applications.
The basic idea is the storage strategy used.
Most designers just note the type of database or databases required, be it a relational or non-relational.
The choice of database depends on economic, type of application or existing infrastructure etc.
The choice of database leads to the overall interaction of the application with the storage device.
Applications are dependent upon memory management (RAM, Cache), file systems, relational and non
relational database systems.
Figure 1.4 Steps 1, 2, and 3
is still storage space free on server 1 and
server 3
Figure 1.5 Old server and new server share the storage system. The new server is intensively tested using the copied production data (4)
Figure 1.6 Finally, the old server is powered down (5) and the new server is started up with the production data (6)
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Most business applications don’t consider the complexity of storage performance factors in their design
activities.
Business applications will show non linear performance.
NON LINEAR PERFORMANCE IN APPLICATIONS
The reasons for non linear performance is due to :
i) The availability of sufficient online storage capacity for application data coupled with sufficient temporary
storage resources. (RAM, Cache etc).
Online storage is the mechanism that allows users to interact with an application, and information is available
in real time.
The amount of online storage required depends on user data, data requirement of the application etc.
When users submit data, there must be locations where the application can temporarily store data before
transaction completes the execution, so RAM, cache are used for temporary storage. (Figure 1.9)
ii) The number of users who will interact with the application and thus access the online storage for application
data retrieval and storage of new data.
The number of user transactions accessing the storage resources corresponds linearly to the amount of time
each transaction takes to complete.
Even in diverse applications, transactions depend on storage infrastructure and also on the server computing
capacity and network capability.
Figure 1.7 Database choices for applications
Figure 1.8 Components that effect application performance
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Therefore configurations can be developed so a fixed number of users will be serviced within an acceptable
response-time window.
Figure 1.10 shows the no of user transactions accessing storage resource will correspond linearly to the amount
of time each transaction takes to complete.
THE CLIENT /SERVER STORAGE MODEL
Figure 1.11 shows the users logged into their client computers and accessing the N/W server. The N/w server is
used to store information and process the same.
The C/S storage model provides data storage capabilities for the server component as well as storage for the
network clients.
When online storage is used with high performance servers, (increased RAM and cache) storage devices are
used by clients for faster access of data.
Servers reach its maximum capacity as client demand increases.
Sharing information on server increased the need for capacity, requiring networks to use multiple servers.
This is due to the need for online storage to handle the growing amount of data. So no of servers increased.
This led to server specialization. The N/W servers had handle clients, keep their profiles & manage N/W
resources which led to the demand for database server.
The relational database model became pervasive; the amount of databases within the N/W grew exponentially.
Figure 1.9 online storage for applications
Figure 1.10 The optimum configuration of user transactions verses
storage resources
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The database server model needed servers to be more robust & powerful. This involved large amounts of RAM,
caches & storage resources.
As data grows storage solutions with client/server storage model continued to be problematic.
Growth rates began to show a varied and asymmetrical growth trend, some servers were deployed with more
storage than required, wasting space or in other cases some servers may not perform due to less space.
Figure 1.13 shows the complexities in data warehouse.
Data warehouse is use as a target market application that ensures customers with good credit are selected &
matched with offerings for financial investments. These matches are stored & targeted for mailings in which
responses are tracked.
The data traverses from online storage “A” on server A, where the customer activity and tracking database
resides, to populate the data warehouse online storage “B” on server DW. The selection of good customers
from server A populates the database on server DW’s online storage “B” where it is matched with financial
investment product offerings also stored on Server A. the aggregate data on C is developed from combining
good customers on server B to from a mailing & tracking list stored on server DW’s online storage “C”.
As data grow, so does user access. The biggest challenge is the internet which is based on the Client/server
storage model.
Web server s began to grow due to the ease of developing web pages, the amount of users able to connect
web server became limited only by addressing and linking facilities.
Figure 1.14 shows how web servers specialize in user access, user profiles & accounts, web pages & mail
Figure 1.11 The client / server storage model
Figure 1.12 Database server configurations
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Internet service providers (ISP) support web based applications & provide access to the internet for the users.
The data traverses from online storage on web server A, where user authentication & access takes place, then
moves to online storage on web user servers where profiles & home pages are stored.
If the request is to check email, the web user transfers the request to the web mail server where request is
placed in an index & transferred to the location of the user’s mail.
If the requested web page is not present in the web server A & B it will locate the web page in the outside
servers & transmit the web page to the customer’s PC.
REACHING THE CLIENT/ SERVER STORAGE LIMITATIONS
Data centric applications, data warehouses & ISPs demonstrate the Client/ Server storage model.
The disk drives are becoming smaller & are holding large amount of data. Caches have advanced. So there
cannot be I/O limitations of Client/ Server architecture.
The amount of servers we have has far exceeded our capability to manage the attached storage.
More & more users are coming online through Internet based capabilities.
Increased functionality & access to a diversity of data has created an informational workplace.
Our own individual demands to store more & more data are pushing the limits of computer networks.
It will be an increasing challenge to accommodate a global online community a global online community
with client/ server storage configurations.
Figure 1.13 Data moving through warehouse application
Figure 1.14 Web Server Storage
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THE BOOT DISK OF INNOVATION
The data flow changes have historically been the “Boot Disk” of innovation. This has prompted the industries to
address the data storage/ data access problems & also to respond to client/ server storage model.
Attempts like combining the elements from the storage world with innovation from the networking
technologies were done by the industries to address the problems.
Thus storage networking was formed, which combines the aspect of previous ideas & technologies in a totally
different manner.
It changes by moving the storage from a “direct” connection to the server to a “Network” connection.
It places the storage directly on the network. It provides a basis for dealing with non linear performance factors
of applications.
It lays foundations for larger data access tasks, share data across servers & management of larger online
storage capacities.
THE BATTLE FOR SIZE AND ACCESS In traditional systems (C/S) storage devices are directly connected to the server (Figure1.15).
All communications with the data stored on the storage devices to be handled by the server, which resulted in
a tremendous overhead on the server.
Storage networks changed this feature by allowing storage devices connected directly to a network.
This created two important changes to traditional storage configurations.
i) It provides direct access paths between storage devices, servers and clients. User transactions can go more
directly to the data. Without unnecessary access to the server.
ii) Storage networking grants business applications greater access to data with increased efficiency.
Storage N/Ws makes it easier to share data, allowing servers to connect to larger amount of data.
Figure 1.15 Directly connected storage
in C/S model
Figure 1.16 NAS showing enhancements to data access
Figure 1.17 SAN showing enhancements to data size
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Storage Networking has 2 models. Network Attached Storage (NAS) & Storage Area Networks (SAN).
NAS allows storage to be placed onto an existing client/ server network based on Ethernet standards using
TCP/ IP protocols (Figure 1.16).
SAN creates a unique network for storage which is based on a protocol called Fibre Channel (Figure 1.17).
METRO DATA AREAS
Our data is stored in large server farms that produce circumstances similar to those in large metropolitan area,
policing, and monitoring performance, security, handling overcrowding & occasional accident.
Powerful servers connected to larger storage systems. The complex network of highways (internet) allows users
to access data regardless of locations or specific storage systems.
Metro data areas will be located in corporate data centers, Internet service provider infrastructures, govt &
public institutions.
Metro data area will have 100% annual growth & will be driven into the next generation of storage technology
which will handle the tremendous amount of data moving in & out of these areas.
WHY STORAGE NETWORKING MAKES SENSE
Why storage networking is needed? (4marks)
Many IT organizations comment on their applications “we have bigger data, more sources and need a single
distribution strategy”.
Bigger data: The data stored and transferred between storage and server is larger in size, the amount of data
transferred between server and client is also larger.
More sources: The application must work on several sources of data to satisfy the client transaction. I.e. server
has to connect with several storage sources.
Single distribution strategy: the results of the application need to be placed in a central location for access.
This means internet accessibility.
THE PROBLEM: SIZE, ACCESS
With the solutions explain the problems faced by IT organizations in terms of Size & Access?
(6marks)
The Problem: Size Many IT organizations say “we must have wider bandwidth for data transfers from storage the
problem is size. The databases we work are exceeding the limitations of the server’s storage connectivity”.
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Wider bandwidth is needed: the connection between server and storage unit requires a faster data transfer
rate. In Client server storage model the data transfer rate is limited to about 10MBPS.
The problem is size: The database and supporting online storage has limitations, resulting in lagging requests
for data & subsequent unresponsive applications.
Solution: Storage networking enables faster data transfers as well as the capability for servers to access larger
data stores.
The Problem: Access
Many IT organizations say “the real problem is access; we don’t have sufficient resources to access the application
server. This will get worse if we go to a single distribution strategy.”
The Problem is Access: There are too many users for the supported configuration. A large number of user
transactions cannot be delivered to the server by the network and cannot be responded in a timely manner.
The single distribution strategy: A single distribution strategy can create an information bottleneck.
Solution: With storage networking, user transactions can access data more directly, bypassing I/O operations
and overhead involved with server.
BUSINESS APPLICATIONS DEFINED FOR STORAGE
Business applications or enterprise business applications will be most affected by and find value in storage
networking. We must first define an enterprise business application, as well as differentiate it from maintenance
applications & support programs.
Enterprise business applications are complex, scalable, distributed & component based.
They are data centric & user friendly. Meets security, administration & maintenance.
There are 3 specific attributes:
Large: Along lived, multiuser, multi developer, multi machine & multi component application that can
manipulate massive data & utilize extensive parallel processing.
Business oriented: To meet specific business requirements, the application encodes business policies, process,
rules& entities is developed in a business organization.
Mission critical: An enterprise business application must be robust enough to sustain continuous operations,
be flexible for scalability & deployment that allows effective maintenance & administration.
MAINTENANCE & SUPPORT APPLICATIONS
Supporting large, highly available business applications & their infrastructures are numerous
maintenance & support applications. They are implemented within support infrastructure areas.
It is important to differentiate between these 2 distinct types of applications.
This difference is important due to IT organizational boundaries that focus on IT specialties between
programming & design personnel.
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The support applications have the following distinct attributes:
Their results are focused upon supporting & maintain server platforms & components that create a continuous
operational infrastructure.
They have enhanced IT abilities to maintain levels of reliability, availability & serviceability for the data center.
The usage of support applications provides necessary information to maintain a scalable & manageable data
center.
The tools & products within these areas defined as storage management applications can be defined by:
Archive/ Backup/ Recovery: Provides IT with tools to initiate data protection policies that copy data & provides
recovery mechanisms.
Storage Resource Management: Enhances the usage of resources that make up the storage infrastructure. It
includes monitoring the stored data.
Storage Data Management: complement the storage infrastructure with enhancements to file/systems, fault
tolerance & data optimization, compression.
Storage Security: it is related to user authentication & resource access technologies.
BUILDING THE BUSINESS APPLICATION
The application designers concentrate on business requirements & produce a requirement document which
determines what will produce to end users at the completion of the development process.
The document which is signed off, will used for external design document which consists of an external view of
end user functions, access points & outputs.
This is followed by internal design activities where the logic & external S/W development components to be
used are identified.
During the internal design process the application designers & programmers work with database administrators
to provide a logical design for application data.
The design is followed by an iterative process of building the application by the application programmers.
Unit testing is performed & then integrated with other components to form a major function of the application
system.
All the components are integrated & tested in terms of system testing, which is followed by user testing where
end users test the system for accuracy& functionality.
Once the system is completely tested the system moves into production mode.
Under production mode certain entities like migrating users from old systems into new systems is seen.
Now it’s a matter how application works with an unknown server& storage infrastructure.
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A third process in the application development cycle is post- implementation analysis & understanding of real
storage & data access requirements of the application system.
The third process requires 2 major pieces of information. First is the availability of storage solutions to offer to
the application designers. Secondly a detailed model understanding of input & output processes.
BENEFITS OF STORAGE NETWORKS ON BUSINESS APPLICATIONS
Briefly discuss the befits of storage networks on business applications (10marks)
(JUNE/JULY 2011)
Scalability of access to business application data:
Figure 1.19 demonstrates the shift from centralized data access to networked data access for SAN & NAS
configurations. Here more servers can connect and utilize storage devices concurrently, thereby reduces the
complexities and overhead involved in maintaining multiple copies of data from each server. Allows centralized access
to the data associated to the application & eliminates single point of failure problem of applications.
Consolidation of business application data:
Since maintaining multiple, synchronized copies of data is no longer necessary, storage devices previously
connected directly to servers are used by more multiple servers. Storage devices can be used more efficiently by
serving multiple servers with multiple sets of data. This eliminates copying and synchronization process and increases
business application availability by decreasing down times.
Figure 1.18 The application development life cycle
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Faster access to Data through improved bandwidth and centralized configurations:
The increased bandwidth associated with moving to storage network configurations has clear advantages in the
amount of data transferred. Here data movement is faster due to the Usage of fiber channel protocol (SAN). NAS
environment also offer increased speed when separate sub network is used. Both the technologies allow for
configurations that can sustain in an increased no of business application transactions.
Increased business application availability through efficiencies in storage management:
Figure 1.20 demonstrates the capabilities of devices with in a SAN configuration to communicate with each other
thereby allowing many of the servers based, data centric maintenance/support applications are optimized. Support
applications are offloaded from the server, i.e. data can be copied from storage network device to another storage
network device (Disk to disk, disk to tape etc). This improves the availability of business applications .In NAS device to
device communication is not possible unlike SAN.
Figure 1.19 Moving to Networked data access with a SAN
Figure 1.20 Device to device communication within a SAN
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