1. Hard Drive Technologies Chapter 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

3. Historical/Conceptual
How Hard Drives Work

4. 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.

5. 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).

6. 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.

7. 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 fluxes
Significantly increased capacity (up to 1TB)

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

9. 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

10. 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

11. 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

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

13. Sectors per Track Number of slices in the hard drive
Stores 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. 1 2 6 3 5 4

14. 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

15. 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 (2^10)
1,083,801,600 / 1024 = 1,058, 400 KB
1,058, 400 KB / 1024 = MB
MB / 1024 = GB

16. 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= bytes (1.44 MB)

17. IT Technician
ATA – The King

18. 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 prominent
Serial ATA (SATA) since 2003
Small Computer System Interface (SCSI)
Pronounced “Scuzzy”
Used in many high-end systems

19. 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
EIDE ATAPI
11.1 MBps to 16.6 MBps
8.4 GB
ATA-3
SMART
ATA-4
Ultra
16.7 MBps to 33.3 MBps
INT13
BIOS Upgrade
137 GB
ATA-5
40-pin 80-wires
ATA/33 ATA/66
44.4 MBps to 6.6 MBps
ATA-6
Big Drive
100 MBps
144 PB
ATA-7
40-pin 80-wires 7-pin
ATA/133 SATA
133 MBps to 300 MBps

20. 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

21. Single
Master
Slave

22. 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 cylinders*16 heads* 63 sectors/track *512 bytes/sector = 528 million bytes
= 504 MB (528 million/ 2^20)

23. 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

24. 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 : 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.

25. 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).

26. 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.

27. 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.

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

29. 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

30. 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

31. 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

32. 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

33. 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 (don’t need jumpers).
Blue connector – to controller
Gray connector – slave drive
Black connector – master drive

34. 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.

35. 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

36. ATA-7 Introduced Ultra DMA 6 Introduced Serial ATA (SATA)
Ultra DMA Mode 6: 133 MBps ATA/133
Used same 40-pin 80 wire cables as ATA-5 and ATA6
Didn’t really take off due to SATA’s popularity
Introduced Serial ATA (SATA)
Increased throughput to 150 MBps to 300 MBps

37. IDE Cables Integrated Drive Electronics Ribbon Rounded No twist!
40 pin
40 pin/80 wires
Max speed = 33MB/sec
Max speed = 133MB/sec

38. 40 wire IDE ribbon cable
33 MB/sec max
80 wire IDE ribbon cable
133MB/sec max

39. 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)

40. Problems with PATA PATA problems: SATA addresses these issues.
IDE cables block airflow and hinder cooling
Max cable length of 18 inches
Can’t 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.

41. 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

42. Serial ATA

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

44. Serial ATA eSATA 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

45. SATA Cable
4-wire data cable
7 pin connector
Motherboard SATA socket

46. SCSI Small Computer System Interface

47. SCSI 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

48. 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

49. SCSI host adapter
PCI host adapter (SCSI controller)

50. 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.

51. 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.

52. 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.

53. 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
Make sure you can look at any SCSI device and understand how to set its SCSI ID!

54. 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 = Off, Off, Off, On
Device 7 = Off, On, On, On
Device 15 = On, On, On, On
Host adapters often set to 7 or 15 but can be changed

55. 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

56. Protecting Data with RAID

57. 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

58. RAID Level 0 Disk Striping Not fault tolerant (not safe)
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

59. 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.

60. RAID Level 1
Mirroring
Duplexing

61. RAID Levels 2 to 4 RAID 2 RAID 3 and 4
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

62. 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

63. RAID 5 (Stripe with Parity)
Decimal 22 21 20 4 2 1 3
Decimal 21 20
Odd Parity 2 1 3 1
Data 1
Data 1
Parity
One of the derive use to store parity.

64. RAID Level 6 Disk Striping with Extra Parity
Its RAID 5 with extra parity information.

65. 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

66. 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.

67. 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

68. 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