OverviewIn this chapter you will learn:

Explain how hard drives workIdentify and explain ATA hard drive

interfacesIdentify and explain SCSI hard drive

interfacesDescribe how to protect data with RAID

Historical/Conceptual

The Hard Drive Hard drives are composed of individual

disks or plattersThe 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.

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).

Data Encoding Hard drives store data in binary form.Binary data stored in tiny magnetic fields

(called fluxesfluxes) that can be placed in either direction.

The flux switches back and forth through a process called flux reversalflux 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.

Data Encoding MethodEncoding methods used by hard driveshard drives are

Run length limited (RLL) 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 fluxesPartial Response Maximum Likelihood Partial Response Maximum Likelihood

(PRML) (PRML) Used by current hard derive.Uses a powerful, intelligent circuitry to

analyze each flux reversalCan have runs of about 16-20 fluxesSignificantly increased capacity (up to

1TB)

Head Actuator

Actuator Arm

Arm Movement in the Hard Drive

Arm Movement in the Hard DriveOnly 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

Geometry GeometryGeometry is used to determine the location

of the data on the hard driveCHS: Cylinders # , Heads # , Sectors #.

If you open hard drive you would not see the geometry.

Used to be critical to know geometryOld day, had to manually enter into CMOS

Today, Geometry stored on hard driveBIOS can query hard drive for geometry

data

HeadsNumber of read/write heads used by the

drive to store dataTwo 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

Cylinders

Cylinder is group of trackstracks of the same diameter going completely through the drive.

Typically hard drive contains thousand of cylinders.

Sectors per Track

Number of slices in the hard driveStores 512 bytes of data.You can’t divide data into any thing

smaller than a sector.Sector per track is value describe # of

sector in each track.

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4 5

6

Obsolete Geometry Might see in older systems

Write pre-compensation cylinder Write pre-compensation cylinder The specific cylinder from where the drive

would start writing data farther apart.Internal sectors were physically smallerExternal sectors physically largerThis identified cylinder where spacing changed

Landing zone Landing zone Unused cylinder as a ‘parking placeparking place’ for headsReferred to as Lzone, LZ, ParkNeeded for older drives using stepper motorsstepper motors

CHS Exercise (1)What is the hard drive capacity with the following

geometry.2100 cyl / 16 heads 63 sectors per track (spt)

AnswerAnswer:C x H x sectors/track x 5122100 x 16 x 63 x 512 = 1,083,801,600 bytes

Each Kilo byte is 1024 byte (2^10)Each Kilo byte is 1024 byte (2^10)

1,083,801,600 / 1024 = 1,058, 400 KB1,058, 400 KB / 1024 = 1033.59375 MB1033.59375 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 51280 x 2 x 18 x 512= 1474560 bytes (1.44

MB)

IT Technician

Hard Drive Interfaces Over years many interface existed for

hard drive.ATA interfaces dominate today’s market

Many changes throughout years.Parallel ATA (PATA) historically prominentSerial ATA (SATA) since 2003

Small Computer System Interface (SCSI)Pronounced “Scuzzy”Used in many high-end systems

ATA Overview

Cable Keywords Speed Max size

ATA-1ATA-1 40-pin PIO and DMA 3.3 MB/s to 8.3MB/s 504 MB

ATA-2ATA-2 40-pin EIDEATAPI

11.1 MBps to 16.6 MBps 8.4 GB

ATA-3ATA-3 40-pin SMART 11.1 MBps to 16.6 MBps 8.4 GB

ATA-4ATA-4 40-pin Ultra 16.7 MBps to 33.3 MBps 8.4 GB

INT13INT13 BIOS Upgrade

137 GB

ATA-5ATA-5 40-pin80-wires

ATA/33 ATA/66

44.4 MBps to 6.6 MBps 137 GB

ATA-6ATA-6 40-pin80-wires

Big Drive 100 MBps 144 PB

ATA-7ATA-7 40-pin80-wires 7-pin

ATA/133

SATA

133 MBps to 300 MBps 144 PB

ATA-1Parallel ATAUsed a single, 40-pin ribbon cable to

connect hard drive to the singlesingle controller on motherboard

Max of 2 drives can attach to a single IDE connector : master and slave

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Single

Master

Slave

ATA-1 Max. Capacity

Supported hard drives up to 504 MB.a max of 1024 cylinders, 16 heads and 63 sectors per track (CHS).1024 cylinders*16 heads* 63 sectors/track

*512 bytes/sector = 528 million bytes= 504 MB (528 million/ 2^20)

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limitation by BIOS

ATA-1 SpeedTo make a Hdrive standard, we must define

both the methodmethod and speedspeed at which the data is going to move: Programmable I/O (PIO) – traditional data traditional data

transfertransfer, 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

PIO and DMA modeDMA 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 0mode 0 : 2.1 MBps Single word DMA mode 1 mode 1 : 4.2 MBps Single word DMA mode 2 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-2Commonly called EIDE -enhanced

Integrated Drive Electronics - (though a misnomermisnomer).

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).

ATA-2 CapacityWith LBA Hdrive lieslies to computer about its

geometry through an advanced type of sector translationsector 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 geometryphysical geometry defined the real layout of

CHS inside drive. Logical geometry Logical geometry described what the drive told

CMOS.

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Sector translationWhen 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. 27

Example of sector translationPhysical 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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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

ATA-3

Introduced Ultra DMA Ultra DMA ModesUltra DMA Mode 0Mode 0: 16.7 MBpsUltra DMA Mode 1Mode 1: 25 MBpsUltra DMA Mode 2Mode 2: 33.3 MBps

Ultra DMA Mode 2, the most popular of ATA-4 DMA model, also called ATA/33

ATA-4

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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Interrupt 13 Extensions (INT 13)

Developed by PhoenixPhoenix TechnologiesPhoenix 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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INT 13 extension

Introduced newer Ultra DMA ModesUltra DMA Mode 3Mode 3: 44.4 MBpsUltra DMA Mode 4Mode 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 (don’t need jumpers). Blue connector – to controller Gray connector – slave drive Black connector – master drive

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-5

“Big Drives” introduced

Replaced INT13 & 24 bit LBA to 48 bit LBA

Increased maximum size to 144 PetaBayte144,000,000 GB

Introduced Ultra DMA 5Ultra DMA Mode 5Mode 5: 100 MBps ATA/100Used same 40-pin 80 wire cables as ATA-5

ATA-6

Introduced Ultra DMA 6Ultra DMA Mode 6: 133 MBps ATA/133Used same 40-pin 80 wire cables as ATA-5 and ATA6Didn’t really take off due to SATA’s popularity

Introduced Serial ATA (SATA)Increased throughput to 150 MBps to 300 MBps

ATA-7

Integrated Drive ElectronicsRibbonRoundedNo twist!40 pin 40 pin/80 wires

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IDE Cables

Max speed = 33MB/sec

Max speed = 133MB/sec

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40 wire IDE ribbon cable33 MB/sec max

80 wire IDE ribbon cable133MB/sec max

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Onboard Controllers(2 x 40 pin male ports)

Primary IDE controller is usually faster – ATA/66, 100

or 133. Secondary controlleroperates at ATA/33

Normally, the IDE controllersIdentified as IDE1 and IDE2

on the motherboard

PATA problems:IDE cables block airflow and hinder coolingMax cable length of 18 inchesCan’t hot-swap PATA drivesTechnology 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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Problems with PATA

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

Serial ATA

Serial ATA More on SATA

◦ SATA is backward compatible.◦ PATA device my be connected to SATA cable using a

SATA bridge

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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7 pin connector

4-wire data cable

Motherboard SATA socket

Pronounced “Scuzzy” Used by specialized server machines. Been around since 70’s 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

SCSI

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

SCSI Chains

SCSI host adapter

PCI host adapter (SCSI controllerSCSI controller)

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 devicesCD-ROM drive is an example of internal SCSI device.

Internal 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.

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.

External Devices

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

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

Setting SCSI IDs

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 both

device at the end of device at the end of cablecable)Most manufacturers

build SCSI devices that self terminate

Termination

The most important part of a PC is the data it holdsCompanies 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 failsRedundant Array of Inexpensive Disks (RAID) is one

such technology

Protecting Data

RAID Level 0Disk 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

Disk Mirroring/Duplexing is the process of writing the same data to two drives at the same timeRequires two drives. What does it means? What does it means?Produces an exact mirror of the primary

driveMirroring uses the same controller.Duplexing uses separate controllers.

Ultimately safe but you lose space.

RAID Level 1

RAID Level 1

DuplexingDuplexingMirroringMirroring

RAID 2Disk Striping with Multiple Parity DrivesNot used

RAID 3 and 4Disk Striping with Dedicated ParityCombined dedicated data drives and dedicated

parity drivesQuickly replaced by RAID 5

RAID Levels 2 to 4

Disk Striping with Distributed ParityDistributes data and parity evenly across the drivesRequires at least 3 drivesMost common RAID implementation

RAID Level 5

Software based RAID 5

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

0

0

1

1

Data

0

1

0

1

Data

1

0

0

1

Parity

One of the derive use to store One of the derive use to store parity.parity.

Disk Striping with Extra Parity

Its RAID 5 with extra parity information.

RAID Level 6

SCSI has been the primary choice in the pastSCSI 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 choiceSpeeds comparable to SCSIDedicated SATA controllers can support up to 15

drives

Implementing RAID

Hardware RAIDUsed when you need speed along with data

redundancy.Need intelligent controller.Invisible to OS Operating system (views it as single views it as single

volumevolume)Most RAID setup in real world are hardware based.

Hardware vs. Software

Software RAIDUsed 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 disksNeeds small software like disk Manager built in Windows server 2003Combines them together as single volume

Hardware vs. Software

ATA RAID controller chips have gone down in price

Some motherboards are now coming with RAID built-in

The Future is RAIDRAID has been around for 20 years but is now less

expensive and moving into desktop systems

Personal RAID