SERVER-CENTRIC IT ARCHITECTURE AND ITS LIMITATIONS In
conventional IT architectures, storage devices are normally
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.
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Server Centric IT Architecture and Its Limitations
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The storage devices 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 architecture is called Server-Centric
IT architecture. In this architecture servers and storage devices
are generally connected together by SCSI (Small Computer System
Interface) cables. www.bookspar.com | VTU NOTES | QUESTION PAPERS |
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In conventional Server-Centric IT architecture storage devices
exist only in relation to the one or two servers to which they are
connected. Failure of both of these computers would make it
impossible to access this data. For companies which manage patient
files, websites etc failure of server is not acceptable as they
need data round the clock. 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. www.bookspar.com | VTU NOTES | QUESTION PAPERS | NEWS | VTU
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Consequently, it is necessary to connect more storage devices
to a computer. This throws up the problem that 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.
Conventional technologies are therefore no longer sufficient to
satisfy the growing demand for storage capacity. www.bookspar.com |
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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 can not use
another storage space attached to another computer.
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storage devices are often scattered throughout an entire
building or branch. Also, 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. www.bookspar.com | VTU NOTES |
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Storage-Centric IT Architecture And Its Advantages 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. www.bookspar.com | VTU NOTES | QUESTION PAPERS | NEWS
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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. www.bookspar.com | VTU NOTES
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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. 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. www.bookspar.com |
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CASE STUDY: REPLACING A SERVER WITH STORAGE NETWORKS In a
production environment an application server is no longer powerful
enough. Then the ageing computer must be replaced by a
higher-performance device. But such a measure can be very
complicated in a conventional, server-centric IT architecture. It
can be carried out very elegantly in a storage network.
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The steps involved in storage network is: 1)Before the
exchange, the old computer is connected to a storage device via the
storage network, which it uses partially 2) 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 kilometres apart. www.bookspar.com | VTU
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3) 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. 4) Then the copied data is
assigned to the new computer and the new computer is tested
intensively. 5) 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. 6) Finally, the new server is restarted with the
production data. www.bookspar.com | VTU NOTES | QUESTION PAPERS |
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Data storage and data access problem The challenge of Designing
Applications: Storing and accessing data depends on the business
application. The basic idea is the storage strategy used. The
choice of database depends on economic, type of application or
existing infrastructure etc.. www.bookspar.com | VTU NOTES |
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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. Business applications will show non
linear performance. www.bookspar.com | VTU NOTES | QUESTION PAPERS
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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 RAM,cache etc are
used for temporary storage. www.bookspar.com | VTU NOTES | QUESTION
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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 correspond linearly to the amount of time
each transaction takes to complete. Even in diverse
applications,transactions depend on storage infrastructure and not
just on the server computing capacity and network capability.
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Client-server storage model 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 and servers. Servers reach its maximum capacity as
client demand increases. When more demand arises,networks use more
servers. www.bookspar.com | VTU NOTES | QUESTION PAPERS | NEWS |
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As data grows storage solutions with client/server storage
model continue to be problematic. For data centric applications,
more storage space is needed. also applications look for server
with more storage space, which may result with wastage of space,or
servers may not perform due to less space. www.bookspar.com | VTU
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