Does science need computer science?

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IBM Systems & Technology Group

| March 2004 |

Disk Drive Science

IBM Systems & Technology Group

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IBM Systems & Technology Group

Data Storage through the ages…



Today we store data on computer disk drives



Previously we used writing on paper



Before that, marks on clay

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IBM Systems & Technology Group

…Grandmothers



Data capacity ~ 100MB ?



Data rate ~ 10b/s



Error rate ?



Reliability ?



Manufacturing cost ?

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IBM Systems & Technology Group

Agenda



Demand for disk storage



What drives areal density?

Aerodynamics

Magnetic recording



Future storage technologies

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IBM Systems & Technology Group

| March 2004 |

Disk Capacity Demand

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IBM Systems & Technology Group

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:

10

9

_{events / sec}

_

_{1PB/s raw data rate}

Hardware filtering to 100MB/s



1PB/yr

By 2008, 15PB/yr

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IBM Systems & Technology Group

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

10

21 B

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IBM Systems & Technology Group

| March 2004 |

Driving Areal density

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IBM Systems & Technology Group

| March 2004 |

Aerodynamics

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Head / Disk interface

Disk Substrate (Aluminium or Glass)

Disk Coating (NiCrMo alloy + 3 atoms Ru)

Slider (Ferrite, Fe/Silicate glass)

Head

Tiny air gap!

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IBM Systems & Technology Group

| March 2004 |

Managing flying height

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Disk Surface Preparation

Head / Slider

Full Surface Texture

Zone Texture

No Texture

Ramp or lift mechanism

Dedicated

landing zone

Smooth

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IBM Systems & Technology Group

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

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IBM Systems & Technology Group

| March 2004 |

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Giant Magnetoresistive effect (GMR)

‘Pinned layer’

_{‘Free layer’}

R

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IBM Systems & Technology Group

Giant Magnetoresistive effect (GMR)

‘Pinned layer’

_{‘Free layer’}

R

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IBM Systems & Technology Group

AntiFerromagnetically Coupled media (“Pixie Dust”)

Demagnetisation energy ~ kT

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IBM Systems & Technology Group

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 10

6

bits



PRML data channel

Partial Response – Maximum Likelihood (look for patterns)



Hard error rates:

‘Server class’ drives (SCSI or Fibre Channel)

1 in 10

15

bits

‘Desktop class’ drives (ATA or S-ATA)

1 in 10

14

bits



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

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IBM Systems & Technology Group

| March 2004 |

The End

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IBM Systems & Technology Group

| March 2004 |

Chemistry

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IBM Systems & Technology Group

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 NbMoTc RuRhPdAgCd In Sn Sb Te I Xe

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

NaMg

Li Be

H

Al

Si

P

S Cl Ar

B C N O F Ne

He

Ce Pr NdPmSmEuGdTbDyHo ErTmYbLu

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IBM Systems & Technology Group

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IBM Systems & Technology Group