Chap72&73

 Explain the various methods of storing and retrieving
images. Compare the advantages and limitations of these
methods.

In This Chapter, you’ll learn on:
 the various storage media
 the advantages and limitations of the various
storage media
 Planning for adequate back-up of data files and
disaster recovery.
 Checking for file integrity and errors.

 Sound Formats for multimedia
About Storage Media
 Without digital storage media like hard disks,
cd’s, dvd’s, servers and so on, your computer
will be just like a standalone video player, only
processing digital signals and nothing more.
 These storage devices are non-volatile,
meaning that they do not require constant
power to store information. Thus they are most
suitable for long term storage of information.
On the opposite side are components like
computer RAM where memory storage is
dynamic but used only temporarily to aid
processes.

 Sound Formats for multimedia About Storage Media
 Most digital storage data devices are accessed sequentially,
thus there will be seek time and latency to access any data
on the devices.
 Of course there are other different kinds of storage devices,
not just those that store your photos, music and other digital
data.

 What is a Tape Media?
 A tape drive is a peripheral hardware
device that reads and writes data into non-
volatile magnetic tapes. A magnetic tape
that resembles a conventional audio
cassette tape, contains a magnetized
coating on a thin plastic strip which data is
written on.
 Unlike dynamic and random storage
mediums such as hard disks and flash
drives, a tape drive operates using indexing
and sequential-access. You have to run a
tape from beginning to the end to perform
a read or write operation. This means that
data is written to the tape in one
continuous stream.

 What is a Tape Media?
 To read a particular piece of information,
the tape must wind past all preceding data
to access it. Quite simply, a tape drive is like
a cassette recorder that stores large
volumes of digital data. Due to its cost
efficiency and long shell life, tape drive
makes a popular device for backup and
archival purposes.

 How Does it Work?
 A tape drive uses a controlled motor to wind the
tape from one reel to another with its magnetic strip
passing a read/write head.
 To cope with the difference between the rate
which data is written into the tape and the data
streaming to or from the computer or host, the tape
drives incorporates a tape drive controller, which
performs buffer procedures and logical operations
such as ECC (Error Correction Code) during the
data storage process.

 During a backup process, the computer memory buffer is
loaded with the data information from the host computer
and sent to the controller's buffer. The controller then
commands the recording mechanism to write the data
into tape. When it completes, more data is loaded into the
controller buffer from the computer and the cycle repeats
itself until all data has been completely stored.
Storage capacity of tape drives range from a few hundred
megabytes to several Terabytes compressed. They support
compression capability and transfer rate of over 500MB/s.
Tape drives are interoperable and usually connected to
the computer via SCSI, IDE, USB and Firewire.

 Tape Drive comes in several formats or standards:
 AIT (Advanced Intelligent Tape)
 AIT is 8mm across and uses helical scanning technique and
the MIC (Memory In Cassette) technology to provide
increased access. It also supports high data transfer rate
up to 78 MB/sec and maximum storage capacity of 500GB
compressed using ALDC (adaptive lossless data
compression) technologies.

 DAT (Digital Audio Tape)
 DAT is 4mm across and offers over 40GB of storage at a
data transfer speed of about 5 Mb per second and is
optimized for high volume backups.
 DLT (Digital Linear Tape)
 DLT uses a technique to write data onto the tape in 128 or
208 linear tracks. DLT cartridges can contain around 70GB
of data with compression. SuperDLT, a new DLT variant
supports tape capacity up to 300GB(SDLT 600) and transfer
data at speeds up to 36MB/sec.

 LTO (Linear Tape-Open)
 LTO uses an open-format technology that provides
compatibility to various storage media products. It supports
a capacity up to 6.4 Terabytes and transfer rate of
540MB/s.
 Packet Tape
 Packet Tape - available from VXA (tape manufacturer) has
a capacity of 33GB native and 66GB compressed. It is an
8mm format and one that is commonly used by home-
based business owners.

 Hard DisksWhat is a Hard Disk?

 Once known as the Winchester drive, the hard disk or hard
drive is an essential hardware that every computer desktop
and server contain. And its functionality, is to store vast
amount of digital data in a non-volatile form, so that data
can be retained when the computer is powered off. Data
is again accessed when the power is on.

 How hard disks work
 Hard disks is a growing storage medium, used in desktop
computers, laptop computers, video recorders, game
consoles, portable players and much more.
 Based on the principles of magnetism much like cassette
tapes and floppy disks, hard drives are not immune to
failure. As such, it is important to take care of your hard
disk, and use it carefully.

 Types of Hard Disks

 There are a few different types of hard disk but, other than
its physical size, the different type of interfaces of the hard
disk is the main difference.
 Types of hard disk interfaces
 • Desktop Hard Disk Types: 3.5', IDE and Sata Interfaces
 • Laptop Hard Disk Types:2.5', 1.8', IDE, Sata, SCSI
 • Server Hard Disk types:3.5' Sata, SCSI

 What are Zip Cartridges?
 Looking akin to their 1.44MB floppy disk predecessors,
IOMEGA zip disks are sized slighter bigger but armed with
the capacity to store over 100 to 700 times more data.
 The Zip data drive was released in the late 1994 by
IOMEGA as a removable storage solution to be used in
mainstream IBM PCs and Macintosh computers. At that
time, as the choices of storage meida are few, Iomega Zip
soon took over the storage market by storm. Due to its
proprietary nature, a zip drive is used to access the disks.

 Beneath the Technology
 There are two distinct features that distinguish a zip disk from a
floppy.
 A zip disk is manufactured with a high quality magnetic
coating which allows its set of read/write head to be
significantly smaller compared to that of a floppy. It uses a
read head positioning mechanism similar to that used in a
hard disk that allows a zip disk to pack thousands of tracks per
inch on the track surface hence by providing a higher real
density.
 Secondly, read and write protection is introduced logically via
a password. Unlike a floppy which implements write protection
on the hardware level, zip disks contain a software meta data
which stores the protection status. Each time a user accesses
the disk, the meta data will be processed and enforced by
the operating system.

 Beneath the Technology
 There are two distinct features that distinguish a zip disk from a
floppy.
 The latest 750MB series supports data transfer rate of about 7.5
MB/s and a 28 milliseconds average seek time as compared
to a standard floppy's 500 Kbit/s transfer rate and several-
hundred millisecond average seek time. Zip disks are also
available in commonly 100MB, 250MB and 750MB sizes.

 What is an Optical Disc?

 An optical disc is a flat piece of circular polycarbonate plastic
containing a non-volatile recording medium that stores digital
information.
 Data is then accessed with a laser diode illuminating on its
recording medium.
 To date, many forms of optical disc have been developed.
Each generally enjoys a span of popularity of use before
newer discs with greater capacity and capability are
introduced into the market.
 Nearing obsolete media includes Laser disc and Video CD
(VCD) while trendy media such a CD (compact disc), CD-R,
CD-RW, DVD-R, DVD-RW continue to thrive in our world of
digital data and storage.

 CD-R
 A CD-R is coated with a photosensitive organic dye
between the polycarbonate substrate and the light
reflective layer. Referred as a WORM (Write Once, Read
Many) media, data can only be written once
permanently.
 Every CD-R contains a spiral groove or track to guide the
movement of the laser beam, provide time measurement
and support various controls during data reading and
writing.
 This track makes about 22,188 revolutions around the disc.

 CD-R
 Coated on one side of the disc with a thin layer of dye and
subsequently with a layer of reflective metal or alloy, a
layer of photo-polymerizable lacquer is applied at the top
to protect the metal reflector from U-V irradiation.
 CD-R is widely used around the world due to its low cost
and availability. It can be accessed by any multimedia
computers or operating system that supports CD-ROM
capability.
 Furthermore, it does not require any special software to
read the media. Due to its nature, it is often used for
archiving purposes.

 How Does CD-R Work?
 A typical CD-R has a storage capacity of 74 minutes of
audio or 650 MB of data.
 Used with a CD-Burner or recorder, users can easily store
music and data files with the ease of popular CD recording
software such as Roxio Easy CD Creator and Ahead Nero.
Windows XP also has its own built-in tool which users can
burn CD using the drag and drop method.

 Recording Process
 The recording begins with the laser indenting small pits (or
tiny indentations) on the dye surface of the disc. The heat
of the laser 'burns' each pit through a chemical reaction,
causing it to become opaque.
 This pit will then reflect less light than the areas that are not
heated by the laser. This irreversible process starts from the
innermost region of the disc to the outermost region.
 When the laser reads the disc, it scans the refractive dye
along the groove and reads the change of reflectivity
which decodes into electrical signals which is subsequently
encoded into binary bits to be processed by the computer.
 So you could see that optical disc is unlike hard disk drives
which store the data on platter as magnetic flux.

 CD-R Writing Speed
 CD-R is manufactured in various write-speed. This value
measures how fast data can be written into the disc by a
CD-Recorder.
 This is also dependent on the capability of CD-Recorders.
CD-Recorders support various speed which is usually
indicated by 3 numbers each separated with a hyphen.
 For example, 40X-24X-48X features that the writer can
support up to a maximum of 40-times write speed, 24-times
rewrite speed and 48-times read speed. 5 years ago, you
could burn a full CD-R in 45 minutes when the first writable
disc was introduced. Today, you can replicate a full CD
within 5 minutes with high speed media.

 CD-R Dye
 The most common organic dye used for manufacturing
CD-R are Cyanine, PhthaloCyanine and Metallized Azo.
 Of all three, Cyanine has the shortest lifespan of about 10
years due to its weak reflection contrast caused by
chemical instability. Cyanine-based CD-Rs are also
susceptible to direct sunlight and are the cause of
common read errors in CD-ROMS.
 Metallized Azo dye is typically blue while PhthaloCyanine
dye comes in silver, gold or transparent in colour. Azo and
PhthaloCyanine are chemically stable and have a longer
shell life.

 CD-RW
 An acronym for Compact Disc Re-Writable, CD-RW is a rewritable
version of a CD or CD-R. With all functionality alike, the CD-RW is
designed to counter the restriction of a CD-R, allowing users to
store, erase, and rewrite new data into the disc.
 Manufacturers have claimed that CD-RW can be reused over a
thousand times. The lifespan of a CD-RW is typically dependent on
the quality of its recording medium and abuse tolerance. Other
attributes include the handling of the disc and the recording
techniques employed by the CD-Burner which writes data into the
disc.

 CD-RW
 Most CD-RW today supports up to a capacity of 700MB of data or
80 minutes of music. UDF or Universal Disk Format is a file system
that can be employed to a CD-RW (CD-R also supports this
feature) to render the disc randomly readable and writable like a
floppy diskette.
 The storage capacity of the disc will however be restricted to
approximately 500MB. This implementation helps users who work
with ever-changing data.

 How Does CD-RW Work?
 A CD-RW contains a phase-change recording medium, usually
made of silver, indium, antimony and tellurium and an aluminium
reflecting layer.
 Alike a CD-R, the laser in the CD-Burner heats the crystal recording
layer and transform it into a non-crystalline amorphous phase. By
controlling the intensity and temperature, crystalline and non-
crystalline areas are formed on the disk.
 Non-crystalline areas will have a poorly reflective contrast
compared to the crystalline areas. Data is hence by marked by
the 'pits' and 'lands' of the disk.

 How Does CD-RW Work?
 When the computer needs to access disc, the laser then read the
disc reflectivity, as it scans along the spiral groove.
 This difference will be registered as digital data, as the light pulses
are decoded into electrical signals which are subsequently
encoded into binary bits to be processed by the computer.
 To erase data on the disc, the laser anneals the recording medium
at a lower temperature and transforming it back into a crystalline
state again.
 Users can continue to reuse the disc until the recording medium
denatures and becomes unusable.

 What is DVD?

 Introduced to the market in year 1997, DVD (also known as Digital
Versatile Disc or Digital Video Disc) has become the latest
generation of optical disc storage technology. Even though it's
physical dimension is the same with compact discs (i.e. 8cm or
12cm in diameter), DVD takes its advantages of having much
higher density with a single data format. Minimum DVD storage of
data is 4.7GB; however its maximum storage capability can be up
to 26 times as much as a standard CD-R. Compared with CD
technology, DVD allows for better quality of graphics, resolution
and surrounded sound. Nowadays, DVD's widespread has gain
support from major numbers of electronic companies, computer
hardware companies, and also music and audio studios all over
the world.

 DVD ARCHITECTURE

 DVD is a 0.6mm thick disc made of poly-carbonate plastic and
has a very much thinner reflective layer made of gold or
aluminium. Two 0.6mm discs are joined together to form a 1.2mm
thick DVD bonded-disc that allows data to be read from either
one side (single-sided) or two sides (double-sided) by laser beam.
 In DVD, lens with higher Numerical Aperture (i.e. NA) is
achieved to refine the laser assembly; hence allow usage of
lesser smaller pits and narrower tracks. Modulation scheme of 8
to 17 (EFM PLUS) is used to provide DVD more efficient
backward compatibility.

 DVD ARCHITECTURE

 Another special and outstanding feature adopted by DVD is the
powerful technique of error correction to recover from even large
scratches with nearly no loss of data. The RS-PC (Reed Solomon
Product Code) is used in this technique which allows as 10 times
more robust than which is currently used in CD system. Also, DVD is
provided with several configurations of data reader ranging from
2D to 3D storage. Each configuration allows different additional
storage capacity.

 DIFFERENT FORMATS OF DVD

 DVD-ROM
 Provide high-capacity computer ROM storage. Data types stored
range from multimedia, computer games, interactive systems to
databases. DVD includes variety of recordable variations
including DVD-R, DVD-RAM, DVD+RW and DVD-RW D-ROM
 DVD-Audio
 Provides far higher quality surround-sound music with increased
playing time.

 DIFFERENT FORMATS OF DVD
 DVD-Video
 Provides high-quality multi-lingual movies on one disk with random-
access to episodes and surround-sound audio.
 What is a Flash Drive?
 Equipped with a NAND-type flash memory and integrated with a
USB 1.1 or 2.0 interface, a flash drive is a removable, compact and
non-volatile data storage device that acts like a portable hard
disk. However unlike the size of the latter, a flash drive is usually no
longer than a cigarette lighter and only weighs half an ounce.

 Mechanics
 Encased in a robust plastic casing, the flash drive contains a small
printed circuit that connects to an embedded flash memory and
a USB connector. This USB connector often protruded out of its
casing to allow the user to plug the drive into the computer's USB
port. For safety purposes, a plastic cap is usually designed to
cover and protect the USB connector.
 When a flash drive is plugged into a computer's USB port, the
system's plug and play capability detects the new hardware and
displays a new logical drive in the My Computer workspace. Users
can then access the drive by double clicking on the drive icon
and simply drag any files across for transmission instantly.

 Developement

 The flash drive was designed for its portability and interoperability
to replace bulky diskettes and CD-RWs that were used to transfer
files between two or more machines.
 Back in 1980, floppy diskettes were popular removable storage
media when file sizes were generally small. Today, a word
document file containing graphics, charts and macro codes can
easily amount to 10MB as compared to a few hundred kilobytes
before 2001. CD-RWs soon replaced the 1.44MB diskettes to
combat the file constraint. However, re-writable discs are
proprietary media that require a CD-writer and software to store
data.
 When the flash drive was made available, it eliminated both
problems and allows machines to read and write data without the
need of any software or peripheral devices.

 Using the Drive
 The flash drive does not require an external power supply.
Essentially, it runs off the small power supplied by the USB
connection and is compatible with any computer that supports
the Universal Serial Bus capability.
 New USB Flash Drives now support transfer rates up to 480 Mbits/s
and storage capacity up to several GB.
 Due to heavy marketing and product branding, flash drives have
been coined and associated with names such as USB drive, key
drive, thumb drive, keychain drive etc.

 What is RAID?

 To understand RAID, imagine multiple disk drives that are put
together and interlinked in an array to obtain greater
performance, capacity and reliability.
 RAID is an acronym for Redundant Array of Independent Disks -
the technique that was developed by researchers at the University
of California at Berkeley during 1987 to overcome the limitation
and deficiency imposed by a single hard disk.

 Using RAID
 RAID became popular when the needs of new applications and
devices are beyond the capability of a typical single hard disk.
Special hard disks are expensive and RAID thus became an
affordable alternative to large storage system that requires
speedy data transfer rates and security.
 RAID is now commonly used on computer server to reliably store
large chunks of data. With the availability of RAID options now
integrated into motherboard chipsets and operating systems,
desktop and high-end users are starting to employ this technology
to operate the storage-intensive tasks, such as non-linear
video/audio editing and critical real-time operations.

 Advantages of RAID Disk
 The key design of RAID is to provide data integrity, fault tolerance,
throughput and expandability.
 RAID can be set to various configurations to increase I/O disk
performances by merging the efficiency of two or more hard
drives into one logical volume or exploiting the redundancy of a
second drive for data replication and integrity.
 Data back up and disaster recovery
 Disaster recovery is the process, policies and procedures related
to preparing for recovery or continuation of technology
infrastructure critical to an organization after a natural or human-
induced disaster. Disaster recovery is a subset of business
continuity. While business continuity involves planning for keeping
all aspects of a business functioning in the midst of disruptive
events, disaster recovery focuses on the IT or technology systems
that support business functions.

 Strategies
 Prior to selecting a disaster recovery strategy, a disaster recovery
planner should refer to their organization's business continuity plan
which should indicate the key metrics of recovery point objective
(RPO) and recovery time objective (RTO) for various business
processes (such as the process to run payroll, generate an order,
etc.). The metrics specified for the business processes must then be
mapped to the underlying IT systems and infrastructure that support
those processes.[4]
 Once the RTO and RPO metrics have been mapped to IT
infrastructure, the DR planner can determine the most suitable
recovery strategy for each system. An important note here however
is that the business ultimately sets the IT budget and therefore the
RTO and RPO metrics need to fit with the available budget. While
most business unit heads would like zero data loss and zero time loss,
the cost associated with that level of protection may make the
desired high availability solutions impractical.

 The following is a list of the most common strategies for data
protection.
  Backups made to tape and sent off-site at regular intervals
  Backups made to disk on-site and automatically copied to off-
site disk, or made directly to off-site disk
  Replication of data to an off-site location, which overcomes
the need to restore the data (only the systems then need to be
restored or synchronized). This generally makes use of storage area
network (SAN) technology
  High availability systems which keep both the data and system
replicated off-site, enabling continuous access to systems and data
 In many cases, an organization may elect to use an outsourced
disaster recovery provider to provide a stand-by site and systems
rather than using their own remote facilities.

 In addition to preparing for the need to recover systems,
organizations must also implement precautionary measures with an
objective of preventing a disaster in the first place. These may
include some of the following:
  Local mirrors of systems and/or data and use of disk protection
technology such as RAID
  Surge protectors — to minimize the effect of power surges on
delicate electronic equipment
  Uninterruptible power supply (UPS) and/or backup generator to
keep systems going in the event of a power failure
  Fire preventions — alarms, fire extinguishers
  Anti-virus software and other security measures

 File integrity monitoring
 File integrity monitoring is an Internal control or Process that performs
the act of assuring Integrity of Operating system and Application
software files using a verification method between the current file
state and the known, good baseline. This comparison method often
involves calculating a known Checksum of the operating system or
file's original baseline and comparing with the calculated checksum
of the current state of the operating system or application file.
 Generally, the act of performing File integrity monitoring is
automated using internal controls such as an application or process.
Such monitoring can be performed randomly, at a defined polling
interval, or in real-time.
 Checking integrity of a file is the best way of telling whether it is
corrupt or not? SFV and MD5 are two common formats used to
check the integrity of files.

 Simple file verification (SFV)
 It is a file format for storing CRC32 checksums of files in order to verify
the integrity of files. SFV can be used to detect random corruptions
in a file, but cannot be used for checking authenticity in any
meaningful way.
 Message-Digest algorithm 5 (MD5)
 It is a widely used cryptographic hash function with a 128-bit hash
value. As an Internet standard (RFC 1321), MD5 has been employed
in a wide variety of security applications, and is also commonly used
to check the integrity of files.

 FlashSFV is a free portable tool for Windows that allows you to
create SFV files and also checks the integrity of files. With it, you can
determine which files are corrupt and which are fine. Note that any
file can be corrupt due to a variety of reasons, including error in
transmissions, write errors, bad flash memory, and so on.

 To create an SFV file using this tool, select New and then select the
files and the output destination to save the SFV file. To check a SFV
file, click Open, select the SFV file and then click Check. There is also
an option to Verify the integrity of files.
 You can associate the SFV and MD5 formats to FlashSFV, add
options in Windows Explorer contextmenu, and change few other
settings by going to Options.
 It is quite an easy-to-use tool when compared with other Integrity
checkers. It works on all versions of Windows.

Chap72&73

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