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Disk Drive Science

Disk Drive Science. IBM Systems & Technology Group Steve P Legg IBM SSG Hursley. 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?.

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Disk Drive Science

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  1. Disk Drive Science IBM Systems & Technology Group Steve P Legg IBM SSG Hursley

  2. 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?

  3. …Grandmothers • Data capacity ~ 100MB ? • Data rate ~ 10b/s • Error rate ? • Reliability ? • Manufacturing cost ? • Maintenance cost ?

  4. Agenda • Demand for disk storage • What drives areal density? • Aerodynamics • Magnetic recording • Future storage technologies N S

  5. Magnetic disk vs. DRAM

  6. Disk Capacity Demand Who needs all this stuff anyway?

  7. 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

  8. 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

  9. Driving Areal density 5 decades of refinement

  10. Inside the head-disk enclosure

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

  12. Aerodynamics “Cruising at an altitude of 0.000001 feet”

  13. Actuator Assembly - close up

  14. Tiny air gap! ~0.0000000200m (200nm) Slider (Ferrite, Fe/Silicate glass) Head Disk Coating (NiCrMo alloy + 3 atoms Ru) Disk Substrate (Aluminium or Glass) Head / Disk interface

  15. Evolution of flying height

  16. The Slider

  17. Managing flying height Demo (if it works)

  18. Disk Surface Preparation Full Surface Texture Head / Slider Dedicated landing zone Zone Texture Smooth data zone No Texture Ramp or lift mechanism

  19. 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)

  20. Magnetic Recording

  21. Magnetic Recording - schematic

  22. ‘Pinned layer’ ‘Free layer’ R Giant Magnetoresistive effect (GMR) More electron scattering Higher resistance

  23. ‘Pinned layer’ ‘Free layer’ R Giant Magnetoresistive effect (GMR) Less electron scattering Lower resistance

  24. Disk Drive Evolution

  25. Where next?

  26. AntiFerromagnetically Coupled media (“Pixie Dust”) Shrink domain size to drive up areal density, but… Demagnetisation energy ~ kT 3 atom layer of Ru

  27. Back to the Future – Punched cards?

  28. Millipede

  29. 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

  30. The End “Thanks for Listening”

  31. Chemistry “What are all these parts made from?”

  32. Elements in a disk drive Printed circuit board Electronics Magnets Mechanical Magnetic coating Electrical connections H He Li Be B C N O O F Ne Na Mg Al Si P S Cl Ar Si Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

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