10. Mass-Storagef12 - S t o r a g e b s i c Role of storage...

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Storage basics
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Role of storage in IT Storage is One of the three major IT infrastructure Computing Networking Storage We often think these as three layers
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Compute , network & storage layer  Applications such as web servers ,data bases etc. live  and run in compute layer  Network layer offers connectivity between computing  nodes eg.  web server talking to database server Storage layer : all data reside in this layer
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Types of storage Persistent storage It does not  loose its content when power is turned off It is standard choice for long term data Eg. Tape, hard disk, flash memory Non persistent It looses data when power is turned off Eg.  Static / dynamic RAM Storage refers to persistent non volatile storage where  memory refers to non persistent technology  
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Supporting technologies  Solid state storage  Upcoming & gaining popularity  Gives excellent performance for random read  workload  Electro-magnetic  storage  Existing for over 50 years Excellent performance for sequential work load 400 MBps : 250 Mbps for 15 K RPM Disk  
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Storage Devices Disk storage : Solid State storage  Tape storage  Hybrid Disk
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IBM RAMAC 350 disk Developed in 1956   Height  66 inches  50 platters of size 24 inches Weight :    around  1 ton Storage capacity : 4MB
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Modern Disk Drives Mechanism Recording Components Rotating Disk  Heads Positioning Components Arm Assembly Track-following System Controller Microprocessor Buffer Memory Interface to SCSI bus
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Magnetic Tape Relatively permanent and holds large quantities of data Random access ~1000 times slower than disk Mainly used for backup, storage of infrequently-used data, transfer medium  between systems 20-1.5TB  typical storage Common technologies are 4mm, 8mm, 19mm, LTO-2 and SDLT
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Disk Attachment Drive attached to computer via  I/O bus USB SATA  (replacing ATA, PATA, EIDE) SCSI  itself is a bus, up to 16 devices on one cable,  SCSI initiator   requests  operation and  SCSI targets   perform tasks  FC  (Fiber Channel) is high-speed serial architecture Can be switched fabric with 24-bit address space – the basis of  storage   area networks   (SAN s )  in which many hosts attach to many storage  units Can be  arbitrated loop (FC-AL)  of 126 devices
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Anatomy of Disk Major components of disk drives Platters  Read write head Actuator assembly Spindle motor  
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Platter Are made up of glass or aluminum substrate Is coated with material It  is rigid, thin,  flat , smooth
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  • Fall '16
  • Operating Systems, Hard disk drive, RAID, disk, Elevator algorithm, Disk read-and-write head, Shortest seek first

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