Disk Drive Science

© 2004 IBM Corporation

IBM Systems & Technology Group

| March 2004 |

Disk Drive Science

IBM Systems & Technology GroupSteve P LeggIBM SSG Hursley


Soton.ac.uk 2004 | Disk Drive Science | © 2004 IBM Corporation

Data Storage through the ages…

Today we store data on computer disk drives

Previously we used writing on paper

Before that, marks on clay

What did mankind use for data storage before the invention of writing?



…Grandmothers

Data capacity ~ 100MB ? Data rate ~ 10b/s Error rate ? Reliability ? Manufacturing cost ? Maintenance cost ?



Agenda

Demand for disk storage What drives areal density?

Aerodynamics

Magnetic recording Future storage technologies

N S



Magnetic disk vs. DRAM



| March 2004 |

Disk Capacity Demand

Who needs all this stuff anyway?



CERN LHC

50 yrs, pure research, technology (NMR, PET, X-ray imaging, WWW)

27km tunnel, 100m below FR/CH 14TeV hadron collider

Scheduled start April 2007

Storage requirements:109 events / sec 1PB/s raw data rate

Hardware filtering to 100MB/s 1PB/yr

By 2008, 15PB/yr

Generate approx 1% of world data production



Disk drive capacity - definitions

B Byte = One letter or number “A” KB Kilobyte = 1000 B (~ few line e-mail) MB Megabyte = 1000 KB (~ Bible or Qu’ran) GB Gigabyte = 1000 MB (~ human

genome) TB Terabyte = 1000 GB (~ Books,

annually) PB Petabyte = 1000 TB (Large companies) EB Exabyte = 1000 PB (Human

knowledge) ZB Zettabyte = 1000 EB 1021B YB Yottabyte = 1000 ZB 1024B



| March 2004 |

Driving Areal density

5 decades of refinement



Inside the head-disk enclosure



Disk Drive Basics Performance: “seek”, “rotational latency”



| March 2004 |

Aerodynamics

“Cruising at an altitude of 0.000001 feet”



Actuator Assembly - close up



Head / Disk interface

Disk Substrate (Aluminium or Glass)

Disk Coating (NiCrMo alloy + 3 atoms Ru)

Slider (Ferrite, Fe/Silicate glass)Head

Tiny air gap!~0.0000000200m (200nm)



Evolution of flying height



The Slider



| March 2004 |

Managing flying height

Demo (if it works)



Disk Surface Preparation

Head / SliderFull Surface Texture

Zone Texture

No TextureRamp or lift mechanism

Dedicatedlanding zone Smooth

data zone



Disk Aerodynamics - summary

Slider “flies”over the disk surface (but very close)

“Air Bearing” is formed by the airflow Slider acts like a racing car in “Ground Effect”

“Landing” in the data zone is a VERY BAD THING TO DO “Head / Disk Interaction” (Head Crash)



| March 2004 |

Magnetic Recording



Magnetic Recording - schematic







Giant Magnetoresistive effect (GMR)

‘Pinned layer’ ‘Free layer’

R

More electron scatteringHigher resistance



Giant Magnetoresistive effect (GMR)

‘Pinned layer’ ‘Free layer’

R

Less electron scatteringLower resistance



Disk Drive Evolution





Where next?



AntiFerromagnetically Coupled media (“Pixie Dust”)

Demagnetisation energy ~ kT3 atom layer of Ru

Shrink domain size to drive up areal density, but…



Back to the Future – Punched cards?



Millipede



A Parting shot – How safe is your data?

[Even IBM] Drives can fail – hence RAID

Density is also limited by error rates Data is a tiny 400MHz signal with S/N ratio close to 1

Soft error rates 1 in 106 bits PRML data channel

Partial Response – Maximum Likelihood (look for patterns) Hard error rates:

‘Server class’ drives (SCSI or Fibre Channel) 1 in 1015 bits

‘Desktop class’ drives (ATA or S-ATA) 1 in 1014 bits

…10% chance of a hard error in reading 1TB for Desktop drives

Unacceptable for most commercial users – hence RAID



| March 2004 |

The End

“Thanks for Listening”



| March 2004 |

Chemistry

“What are all these parts made from?”



Elements in a disk drive

Cs Ba La Hf Ta W ReOs Ir Pt AuHg Tl Pb Bi Po At Rn

Rb Sr Y Zr NbMoTcRuRhPdAgCd In Sn Sb Te I Xe

K Ca Sc Ti V CrMnFe Co Ni CuZnGaGeAs Se Br Kr

NaMg

Li Be

H

Al PSi S Cl Ar

B C N O F Ne

He

Ce Pr NdPmSmEuGdTbDyHo ErTmYbLu

Printed circuit boardElectronicsMagnetsMechanicalMagnetic coatingElectrical connections

Si

O

Si







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Disk Drive Science