ch12 - Chapter 12: Mass-Storage Systems Chapter 12:...

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Unformatted text preview: Chapter 12: Mass-Storage Systems Chapter 12: Mass-Storage Systems Adapted to COP4610 by Robert van Engelen 12.2 Silberschatz, Galvin and Gagne 2005 Operating System Concepts 7 th Edition, Jan 1, 2005 Overview of Mass Storage Structure: Tape Overview of Mass Storage Structure: Tape Magnetic tape Early secondary-storage medium Relatively permanent and holds large quantities of data Access time slow Random access ~1000 times slower than disk Mainly used for backup, storage of infrequently-used data, transfer medium between systems Kept in spool and wound or rewound past read-write head Once data under head, transfer rates comparable to disk 20-200GB typical storage Common technologies are 4mm, 8mm, 19mm, LTO-2 and SDLT 12.3 Silberschatz, Galvin and Gagne 2005 Operating System Concepts 7 th Edition, Jan 1, 2005 Overview of Mass Storage Structure: Disk Overview of Mass Storage Structure: Disk Magnetic disks provide bulk of secondary storage of modern computers Drives rotate at 60 to 200 times per second 3,600 -12,000 RPM Transfer rate is the rate at which data flows between drive and computer Positioning time ( random-access time ) is time to move disk arm to desired cylinder ( seek time ) and time for desired sector to rotate under the disk head ( rotational latency ) Head crash results from disk head making contact with the disk surface Thats bad 12.4 Silberschatz, Galvin and Gagne 2005 Operating System Concepts 7 th Edition, Jan 1, 2005 Overview of Mass Storage Structure: Disk Overview of Mass Storage Structure: Disk Disks can be removable, mounted as needed Drive attached to computer via I/O bus Busses vary, including EIDE, ATA, SATA, USB, Fiber Channel, SCSI, and FireWire Host controller in computer uses bus to talk to disk controller built into drive or storage array 12.5 Silberschatz, Galvin and Gagne 2005 Operating System Concepts 7 th Edition, Jan 1, 2005 Disk Structure Disk Structure Disk drives are addressed as large 1-dimensional arrays of logical blocks The logical block is the smallest unit of transfer, usually 512 bytes The array of logical blocks is mapped into the sectors of the disk sequentially Sector 0 is the first sector of the first track on the outermost cylinder Mapping proceeds in order through that track, then the rest of the tracks in that cylinder, and then through the rest of the cylinders from outermost to innermost Moving-head disk mechanism 12.6 Silberschatz, Galvin and Gagne 2005 Operating System Concepts 7 th Edition, Jan 1, 2005 Disk Attachment Disk Attachment Host-attached storage accessed through I/O ports talking to I/O busses SCSI itself is a bus, up to 16 devices on one cable, SCSI initiator requests operation and SCSI targets perform tasks Each target can have up to 8 logical units (disks attached to device controller FC is high-speed serial architecture Can be switched fabric with 24-bit address space the...
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This note was uploaded on 10/11/2011 for the course COP 4610 taught by Professor Robertengelen during the Spring '11 term at FSU.

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ch12 - Chapter 12: Mass-Storage Systems Chapter 12:...

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