Hard Drive Technologies Chapter 9

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Hard Drive TechnologiesChapter 9
2
Overview

• In this chapter you will learn
• Explain how hard drives work
• Identify and explain ATA hard drive interfaces
• Identify and explain SCSI hard drive interfaces
• Describe how to protect data with RAID

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How Hard Drives Work
Historical/Conceptual
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The Hard Drive

• Hard drives are composed of individual disks or
  platters
• The platters are made up of aluminum
  (non-magnetic), and are coated with a magnetic
  medium
• Two tiny read/write heads service each platter
  one to read top and the other to read bottom.

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The Hard Drive

• The closer the read/write heads are to the
  platter, the more densely the data can be packed
  on to the drive.
• Hard drives use a tiny, heavily filtered aperture
  to equalize the air pressure between the exterior
  and interior of the hard drive (sensitive for
  dust).
• Platters spin between 3500 and 10,000 rounds per
  minute (RPM).

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Data Encoding

• Hard drives store data in binary form.
• Binary data stored in tiny magnetic fields
  (called fluxes) that can be placed in either
  direction.
• The flux switches back and forth through a
  process called flux reversal
• Fluxes in one direction are read as 0 and the
  other direction as 1
• Hard drives read these flux reversals at a very
  high speed when accessing or writing data using
  encoding method.

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Data Encoding Method

• Encoding methods used by hard drives are
• Run length limited (RLL)
• Instated of dealing with individual fluxes HD
  read and write group of flux called run. That are
  unique patterns of ones and zeros
• Can have runs of about 7 fluxes
• Partial Response Maximum Likelihood (PRML)
• Used by current hard derive.
• Uses a powerful, intelligent circuitry to analyze
  each flux reversal
• Can have runs of about 16-20 fluxes
• Significantly increased capacity (up to 1TB)

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Arm Movement in the Hard Drive
Head Actuator
Actuator Arm
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Arm Movement in the Hard Drive

• Only two technologies used for moving the
  actuator arm.
• 1- The stepper motor technology
• Moves the arms in fixed increments or steps
• Arms parked in non-data area using special
  parking program.
• Only seen in floppies today.
• 2- The voice coil or linear motor technology
• Uses a permanent magnet surrounding the coil on
  the actuator arm to move the arm.
• When an electrical current passes the coil
  generates a magnetic filed that moves an actuator
  in both direction.
• Automatically parks drive over non-data area when
  power removed

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Geometry

• Geometry is used to determine the location of the
  data on the hard drive
• CHS Cylinders , Heads , Sectors .
• If you open hard drive you would not see the
  geometry.
• Used to be critical to know geometry
• Old day, had to manually enter into CMOS
• Today, Geometry stored on hard drive
• BIOS can query hard drive for geometry data

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Heads

• Number of read/write heads used by the drive to
  store data
• Two heads per platter (top and bottom)
• Most hard drives have an extra head or two for
  their own usage, so the number may not be even

This is track
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Cylinders

• Cylinder is group of tracks of the same diameter
  going completely through the drive.
• Typically hard drive contains thousand of
  cylinders.

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Sectors per Track

• Number of slices in the hard drive
• Stores 512 bytes of data.
• You cant divide data into any thing smaller than
  a sector.
• Sector per track is value describe of sector in
  each track.

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2
6
3
5
4
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Obsolete Geometry

• Might see in older systems
• Write pre-compensation cylinder
• The specific cylinder from where the drive would
  start writing data farther apart.
• Internal sectors were physically smaller
• External sectors physically larger
• This identified cylinder where spacing changed
• Landing zone
• Unused cylinder as a parking place for heads
• Referred to as Lzone, LZ, Park
• Needed for older drives using stepper motors

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CHS Exercise (1)

• What is the hard drive capacity with the
  following geometry.
• 2100 cyl / 16 heads 63 sectors per track (spt)
• Answer
• C x H x sectors/track x 512
• 2100 x 16 x 63 x 512 1,083,801,600 bytes
• Each Kilo byte is 1024 byte (210)
• 1,083,801,600 / 1024 1,058, 400 KB
• 1,058, 400 KB / 1024 1033.59375 MB
• 1033.59375 MB / 1024 1.009 GB

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CHS Exercise (2)

• A "1.44 MB floppy disk has
• 80 cylinders, 2 heads and 18 sectors/track.
• Therefore, its capacity in sectors is computed as
  follows
• C x H x sectors x 512
• 80 x 2 x 18 x 512 1474560 bytes (1.44 MB)

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ATA The King
IT Technician
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Hard Drive Interfaces

• Over years many interface existed for hard drive.
• ATA interfaces dominate todays market
• Many changes throughout years.
• Parallel ATA (PATA) historically prominent
• Serial ATA (SATA) since 2003
• Small Computer System Interface (SCSI)
• Pronounced Scuzzy
• Used in many high-end systems

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ATA Overview
Cable Keywords Speed Max size
ATA-1 40-pin PIO and DMA 3.3 MB/s to 8.3MB/s 504 MB
ATA-2 40-pin EIDEATAPI 11.1 MBps to 16.6 MBps 8.4 GB
ATA-3 40-pin SMART 11.1 MBps to 16.6 MBps 8.4 GB
ATA-4 40-pin Ultra 16.7 MBps to 33.3 MBps 8.4 GB
INT13 BIOS Upgrade 137 GB
ATA-5 40-pin80-wires ATA/33 ATA/66 44.4 MBps to 6.6 MBps 137 GB
ATA-6 40-pin80-wires Big Drive 100 MBps 144 PB
ATA-7 40-pin80-wires 7-pin ATA/133SATA 133 MBps to 300 MBps 144 PB
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ATA-1

• Parallel ATA
• Used a single, 40-pin ribbon cable to connect
  hard drive to the single controller on
  motherboard
• Max of 2 drives can attach to a single IDE
  connector master and slave

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Single
Master
Slave
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ATA-1 Max. Capacity
limitation by BIOS

• Supported hard drives up to 504 MB.a max of 1024
  cylinders, 16 heads and 63 sectors per track
  (CHS).
• 1024 cylinders16 heads 63 sectors/track 512
  bytes/sector 528 million bytes
• 504 MB (528 million/ 220)

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ATA-1 Speed

• To make a Hdrive standard, we must define both
  the method and speed at which the data is going
  to move
• Programmable I/O (PIO) traditional data
  transfer, is an I/O addressing scheme where CPU
  talks directly to Hdrive via BIOS to send and
  receive data.
• 3.3 MB/s to 8.3 MB/s
• DMA Direct Memory Access
• 2.1 MB/s to 8.3 MB/s
• Called PIO Mode and DMA Mode

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PIO and DMA mode

• DMA modes defined a method to enable Hdrives to
  talk to RAM directly using old-style DMA commands
  (called single word DMA)
• 3 ATA single word DMA modes (which were slow)
• Single word DMA mode 0 2.1 MBps
• Single word DMA mode 1 4.2 MBps
• Single word DMA mode 2 8.3 MBps
• At boot BIOS queried Hdrive to see what modes it
  could use and would then automatically adjust to
  the fastest mode.

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ATA-2

• Commonly called EIDE -enhanced Integrated Drive
  Electronics - (though a misnomer).
• Added second controller to allow for four drives
  instead of only two.
• Added ATAPI that enabled non-hard drive device
  such as CD-ROM to connect to the PC via ATA-2
  controllers.
• Broke the 504 MB barrier using Logical Block
  Addressing (LBA).

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ATA-2 Capacity

• With LBA Hdrive lies to computer about its
  geometry through an advanced type of sector
  translation.
• To get up to 8.4 GB instead of 504 MB
• So, the ATA-2 spec was designed to have 2
  geometries
• the physical geometry defined the real layout of
  CHS inside drive.
• Logical geometry described what the drive told
  CMOS.

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Sector translation

• When data was being translated to and from the
  drive, the onboard circuitry of the derive
  translated the logical geometry into the physical
  geometry.
• Since the BIOS CHS allows for fewer cylinders,
  the actual cylinders reported by the drive are
  divided by 2, 4, 8, or 16 to bring the number
  below 1024 and the number of heads is multiplied
  by that same number.

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Example of sector translation
Physical CHS Parameters Logical CHS Parameters
Cylinders 12,000 750
Heads 16 256
Sectors/Track 63 63
Total Sectors 12,096,000 12,096,000
Capacity 6,193MB 6,193MB
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ATA-3

• Self-Monitoring Analysis and Reporting Technology
• S.M.A.R.T.
• Helps predict when a hard drive is going to fail
  by monitoring the hard drives mechanical
  components.
• No real change in other stats

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ATA-4

• Introduced Ultra DMA Modes
• Ultra DMA Mode 0 16.7 MBps
• Ultra DMA Mode 1 25 MBps
• Ultra DMA Mode 2 33.3 MBps
• Ultra DMA Mode 2, the most popular of ATA-4 DMA
  model, also called ATA/33

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Interrupt 13 Extensions (INT 13)

• The original ATA-1 standard allowed for hard
  drives up to 137 GB!
• 504 MB limit was caused by old AT BIOS , AND BIOS
  not ATA standard could support only 504 MB.
• LBA was a work-around that told Hdrive to lie to
  BIOS to get it up to 8.4 GB
• Eventually Hdrives started edging close to LBA
  limit. BIOS makers needed to fix BIOS. It was
  done by a new set of BIOS commands called INT13
  extensions

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INT 13 extension

• Developed by Phoenix Technologies
• Phoenix came up with a new set of BIOS commands
  called Interrupt 13 extension.
• It broke the 8.4 GB barrier by ignoring CHS
  values and feeding LBA a stream of addressable
  sectors
• BIOS must recognize INT 13

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ATA-5

• Introduced newer Ultra DMA Modes
• Ultra DMA Mode 3 44.4 MBps
• Ultra DMA Mode 4 66.6 MBps
• Ultra DMA Mode 4 is the most popular also called
  ATA/66
• Used 40 pin cable, but had 80 wires
• ATA-5 defined exactly where the controller
  master and slave drives connected (dont need
  jumpers).
• Blue connector to controller
• Gray connector slave drive
• Black connector master drive

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ATA-5

• ATA/66 is backward compatible.
• You can safely plug an earlier drive into an
  ATA/66 cable and controller.
• if you plug an ATA/66 drive into an older
  controller , it will work (but not in ATA/66
  mode).
• The only risky action is to use an ATA/66
  controller and Hdrive with a non-ATA/66 cable. It
  causes data losses.

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ATA-6

• Big Drives introduced
• Replaced INT13 24 bit LBA to 48 bit LBA
• Increased maximum size to 144 PetaBayte
• 144,000,000 GB
• Introduced Ultra DMA 5
• Ultra DMA Mode 5 100 MBps ATA/100
• Used same 40-pin 80 wire cables as ATA-5

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ATA-7

• Introduced Ultra DMA 6
• Ultra DMA Mode 6 133 MBps ATA/133
• Used same 40-pin 80 wire cables as ATA-5 and ATA6
• Didnt really take off due to SATAs popularity
• Introduced Serial ATA (SATA)
• Increased throughput to 150 MBps to 300 MBps

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IDE Cables

• Integrated Drive Electronics
• Ribbon
• Rounded
• No twist!
• 40 pin
• 40 pin/80 wires

Max speed 33MB/sec
Max speed 133MB/sec
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40 wire IDE ribbon cable 33 MB/sec max
80 wire IDE ribbon cable 133MB/sec max
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Motherboard Connections
Primary IDE controller is usually faster
ATA/66, 100 or 133. Secondary controller operates
at ATA/33
Normally, the IDE controllers Identified as IDE1
and IDE2 on the motherboard
Onboard Controllers (2 x 40 pin male ports)
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Problems with PATA

• PATA problems
• IDE cables block airflow and hinder cooling
• Max cable length of 18 inches
• Cant hot-swap PATA drives
• Technology has reached the limits of what it can
  do in terms of throughput
• SATA addresses these issues.
• SATA derives transfer data in serial bursts
  instead of parallel.

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Serial ATA

• Serial ATA (SATA) creates a point-to-point
  connection between the device and the controller
• Hot-swappable
• Can have as many as 8 SATA devices
• Thinner cables resulting in better air flow and
  cable control in the PC
• Maximum cable length of 40 inches (1 meter)
  compared to 18 inches for PATA cables

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Serial ATA
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Serial ATA

• More on SATA
• SATA is backward compatible.
• PATA device my be connected to SATA cable using a
  SATA bridge

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Serial ATA

• More on SATA
• Can have as many as 8 SATA devices
• Add more SATA functionality via a PCI card
• eSATA
• External SATA
• Extends SATA bus to external devices

eSATA Port
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SATA Cable
4-wire data cable
7 pin connector
Motherboard SATA socket
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SCSISmall Computer System Interface

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SCSI

• Pronounced Scuzzy
• Used by specialized server machines.
• Been around since 70s
• Devices can be internal or external
• Historically the choice for RAID
• Faster than PATA
• Could have more than 4 drives
• SATA replacing SCSI in many applications

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SCSI Chains

• SCSI devices connect together in string of device
  called chain.
• The host adapter is a device that attaches the
  SCSI chain to the PC
• All SCSI devices are divided into internal and
  external groups
• The maximum number of devices, including the host
  adapter, is 16

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SCSI host adapter

• PCI host adapter (SCSI controller)

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Internal Devices

• Internal SCSI devices are installed inside the PC
  and connect to the host adapter through the
  internal connector
• Internal devices use a 68-pin ribbon cable. Flat
  and flexible cable.
• Cables can be connected to multiple devices
• CD-ROM drive is an example of internal SCSI
  device.

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External Devices

• External SCSI devices are connected to host
  adapter to external connection of host adapter
• D shape connector.
• Many external devices connect to the host adapter
  with
• 50-pin high density (HD) connector.
• Higher end SCSI device use 68-pin HD connector
  like internal device.

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External Devices

• External devices have two connections in the
  back, to allow for daisy-chaining
• process of connecting device directly to anther
  device is called daisy chaining
• You can daisy chain up to 15 device to one host
  adapter.
• These device can be internal or external or both.

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SCSI IDs

• Each SCSI device must have a unique SCSI ID
• The values of ID numbers range from 0 to 15
• No two devices connected to a single host adapter
  can share the same ID number
• There is no order for the use of SCSI IDs, and
  any SCSI device can have any SCSI ID

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Setting SCSI IDs

• The SCSI ID for a particular device can be set by
  configuring jumpers, switches or even dials
• Make sure you can look at any SCSI device and
  understand how to set its SCSI ID!
• Use your hexadecimal knowledge to set the device
  ID
• Device 1 0 0 0 1 Off, Off, Off, On
• Device 7 0 1 1 1 Off, On, On, On
• Device 15 1 1 1 1 On, On, On, On
• Host adapters often set to 7 or 15 but can be
  changed

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Termination

• Terminators are used to prevent a signal
• reflection which can corrupt the signal
• Pull-down resistors are usually used as
  terminators
• Only the ends of the SCSI chains need to be
  terminated (both
• device at the end of
• cable)
• Most manufacturers build SCSI devices that self
  terminate

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Protecting Data with RAID

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Protecting Data

• The most important part of a PC is the data it
  holds
• Companies have gone out of business because of
  loosing the data on their hard drive
• Hard drives will eventually develop faults
• Fault tolerance allows systems to still operate
  even when a component fails
• Redundant Array of Inexpensive Disks (RAID) is
  one such technology

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RAID Level 0

• Disk Striping
• Spreading the data among multiple drive.
• Requires at least 2 hard drives.
• Provides increased read and writes (faster).
• Not fault tolerant (not safe)
• If any drive fails, the data is lost

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RAID Level 1

• Disk Mirroring/Duplexing is the process of
  writing the same data to two drives at the same
  time
• Requires two drives. What does it means?
• Produces an exact mirror of the primary drive
• Mirroring uses the same controller.
• Duplexing uses separate controllers.
• Ultimately safe but you lose space.

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RAID Level 1
Duplexing
Mirroring
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RAID Levels 2 to 4

• RAID 2
• Disk Striping with Multiple Parity Drives
• Not used
• RAID 3 and 4
• Disk Striping with Dedicated Parity
• Combined dedicated data drives and dedicated
  parity drives
• Quickly replaced by RAID 5

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RAID Level 5

• Disk Striping with Distributed Parity
• Distributes data and parity evenly across the
  drives
• Requires at least 3 drives
• Most common RAID implementation

Software based RAID 5
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RAID 5 (Stripe with Parity)
Decimal 22 21 20
4 2 1
0 0 0 0
1 0 0 1
2 0 1 0
3 0 1 1
4 1 0 0
Decimal 21 20 OddParity
2 1
0 0 0 1
1 0 1 0
2 1 0 0
3 1 1 1
One of the derive use to store parity.
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RAID Level 6

• Disk Striping with Extra Parity
• Its RAID 5 with extra parity information.

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Implementing RAID

• SCSI has been the primary choice in the past
• SCSI chaining of multiple device to single
  controller made it natural for RAID.
• Faster than PATA
• PATA only allowed 4 drives
• SATA today viewed as comparable choice
• Speeds comparable to SCSI
• Dedicated SATA controllers can support up to 15
  drives

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Hardware vs. Software

• Hardware RAID
• Used when you need speed along with data
  redundancy.
• Need intelligent controller.
• Invisible to OS Operating system (views it as
  single volume)
• Most RAID setup in real world are
• hardware based.

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Hardware vs. Software

• Software RAID
• Used when price takes priority over performance.
• Does not required special controllers.
• You can use ATA controller or SCSI host adapter.
• Operating system recognizes all
• individual disks
• Needs small software like disk
• Manager built in Windows server 2003
• Combines them together as single volume

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Personal RAID

• ATA RAID controller chips have gone down in price
• Some motherboards are now coming with RAID
  built-in
• The Future is RAID
• RAID has been around for 20 years but is now less
  expensive and moving into desktop systems