itp 101 introduction to information technologytrinagre/itp101/lectures/itp101_storage.pdf · •...
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ITP 101 Introduction to Information
Technology Storage
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Overview • Secondary Storage
– Magnetic Media • Floppy Disks • Hard Disks
– Files & fragmentation – RAID
– Optical Storage – Flash Memory
• Cloud Storage
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• Why do we need to know this stuff in detail? – To show the computer support guy you know
what you’re talking about J – Databases – Computer Forensics – Recovering your deleted files!
Storage
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Floppy Disk • Data storage medium
– composed of a disk of thin, flexible ("floppy") magnetic storage medium – sealed in a square or rectangular plastic carrier lined with fabric that
removes dust particles • Read and written by a floppy disk drive (FDD) • Invented by IBM • 3 sizes – 8", 5 ¼", and 3 ½" • Used from the mid-1970s to
the late 1990s • 8-track of removable media • By 1996, there were an estimated five billion floppy disks in use
• Max storage for 3 ½" floppy disk in 1997 was 240 MB
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• Disk is broken down into Tracks and Sectors – Track – Concentric ring around the disk – Sector – Pie-shaped wedge section of the disk
• It is the smallest unit that can be obtained at once from a disk • Cannot retrieve one byte at a type, must retrieve one sector
at a time
Floppy Disk – Storing Data
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Floppy Disk – Reading & Writing • A small motor in the drive rotates the diskette at a regulated speed • A second motor-operated mechanism moves the magnetic read–
write head along the surface of the disk • Both read and write operations require physically contacting the
read–write head to the disk media, an action accomplished by a "disk load" solenoid.
• To write data: – Current is sent through a coil in the head – The magnetic field of the coil magnetizes spots on the disk as it rotates;
the change in magnetization encodes the digital data. • To read data:
– The tiny voltages induced in the head coil by the magnetization on the disk are detected, amplified by the disk drive electronics, and sent to the Floppy disk controller
– The controller separates the data from the stream of pulses coming from the drive, decodes the data, tests for errors, and sends the data on to the host computer system.
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Geek Joke
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• Where most of your data is saved on your computer
• Internal persistent storage device • Invented in the 1950s • A typical desktop machine will have a hard disk
with a capacity of between 40 and 200 gigabytes • Data is stored onto the disk in the form of files
– A file is simply a named collection of bytes • Contains 3-5 magnetized platters spinning 5400+
revolutions per minute (RPM) • 98% of magnetic hard disk market dominated by
Western Digital and Seagate
Hard Disks
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Hard Disk – Inside http://www.pantherproducts.co.uk/Articles/What_is/What_is_Hard_Disk.shtml
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• Logical breakdown of a hard disk – Tracks
• Like tracks on an LP or a CD • Rings that go completely around the center of the
platter – Sectors
• Pie-shaped wedges of tracks • Multiple sectors = 1 track • 512 bytes for magnetic media, 2048 bytes for optical
media – Cylinders
• All tracks that line up on parallel platters • Multiple tracks = 1 cylinder
Hard Drive Logically
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Tracks, Cylinders, and Sectors
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• Why does my paper take up 4 KB of hard disk space when it is only a page long? – Windows file systems break down the hard disk into
clusters. Each file can use one or more clusters. • 1 sector = 512 bytes • 1 cluster = 8 sectors (default)
= 4096 bytes = 4 KB – The smallest a file can be (typically) is 4 KB – All files have sized in multiples of 4 KB
• File fragmentation – Clusters do not need to be consecutive – “Defragmenting” the hard disk will attempt
to place all clusters in consecutive order for files
Files and File Fragmentation
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• Probably didn’t – Possible to recover evidence and files off of
people’s systems that have “crashed” • Read/write heads are extremely close to the
platters – “Liquid ball bearings” – If the head makes contact with the platter, called
a “head crash”, and it will destroy your data • Possible to take the platters out of the drive
and place them in a new drive – Needs a clean room
My hard disk crashed!
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• Redundant Array of Independent Disks – Nowadays, it is called a “Redundant Array of Inexpensive Disks”
• Takes 2 or more physical hard disks and makes it look like one hard disk to the computer and user
• Umbrella term for computer data storage schemes that can divide and replicate data among multiple disk drives
• The various designs of RAID systems involve two key goals: – Increase data reliability – Increase input/output performance
• Advantages: – Larger capacity and faster access
• Disadvantage: – More points of failure
RAID
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RAID 0, RAID 1, RAID 5
• Many RAID levels employ an error protection scheme called "parity" • Most use the simple XOR (exclusive or) parity
– Meaning "one or the other, but not neither or both”
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RAID 0 RAID 1 RAID 5 Description Block-level striping
without parity or mirroring
Mirroring without parity or striping
Block-level striping with distributed parity
Minimum # of disks 2 2 3 Fault tolerance No Yes Yes Speed Increase Yes No Yes Total storage* Two 200GB Drives
= 400 GB Two 200GB Drives = 400 GB
Three 200GB Drives = 600 GB
Total data storage* 400 GB 200 GB 400 GB
RAID 0, RAID 1, RAID 5
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A1 – D3 represent blocks of data Ap – Dp represent parity data
• Instead of using polarized charge, it uses reflective pits – “Lands” – flat areas of the
disk – “Pits” – parts of the disk that
take a different time to reflect the light
• The time to reflect back to the source determines whether a 1 or a 0 was read
Optical Media
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• CD-ROM – Granddaddy of them all – Developed by Sony and Phillips – Commercially available since October 1982 – 650 MB, 74 minutes of audio (thanks to Beethoven’s 9th symphony) – Created for distributing audio
• DVD – Digital versatile disc or digital video disc – Available in US since March 1997 – 4.7 GB for single layer, single sided – Created for distributing video
• Blu-Ray – Created for distributing high-definition video – Officially released in June 2006 – 25 or 50 GB discs
Optical Media
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Blu-ray Disc, DVD, & CD
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• Used in USB flash (aka. thumb) drives, digital cameras, solid state drives, and MP3 players
• Type of EEPROM – electrically erasable programmable read-only memory
• Uses electrical signals and current to store memory – similar to RAM
• More reliable than magnetic media • No moving parts • Lifetime is an issue • Flash memory as a replacement for hard drives
– Used in Apple's MacBook Air, iPhone & iPad • In 2008, the flash memory industry
includes about US$9.1 billion in production and sales
Flash Memory
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Floppy / Flash Comparison SD memory card • 32 GB • $20 • $0.0006 / MB • $0.63 / GB
Floppy Disk • 1.44 MB • $0.80 • $0.55 / MB • $569 / GB
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Source: Amazon.com (April 2013)
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Cloud Storage • Instead of data residing on a local storage
device, it is stored online for you in large data centers – Data is typically synced to multiple hard drives
by the storage provider – Data is pushed by the
internet to multiple devices • Becoming very popular with
enterprises and companies
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Cloud Storage • Advantages
– Pricing directly related to the amount stored • No wasted space
– Data is synced across multiple devices by the cloud provider
• Typically no data loss
• Disadvantages – You do not control your data – Security & Privacy Issues
• Encryption becomes very important – If the provider is compromised (hacked), then your data is
compromised
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Cloud Storage Providers
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Cloud Storage Pricing • Dropbox – 2GB Free, $99/yr for 100GB • iCloud – 5GB Free, $100/yr for 50GB • SkyDrive – 7GB Free, $50/yr for 100GB • Google Drive – 5GB Free, $60/yr for 100GB • 500 GB External Hard Drive - $60
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