mass storage structures (13)

mass storage structures (13) - COP 4600 Summer 2011...

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COP 4600: Intro To OS (Mass Storage Systems) Page 1 © Dr. Mark Llewellyn COP 4600 – Summer 2011 Introduction To Operating Systems Mass Storage Systems Department of Electrical Engineering and Computer Science Computer Science Division University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cop4600/sum2011
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COP 4600: Intro To OS (Mass Storage Systems) Page 2 © Dr. Mark Llewellyn Overview of Mass Storage Structure Magnetic disks provide bulk of secondary storage of modern computers Drives rotate at 60 to 200 times per second Transfer rate is rate at which data flow 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 That’s bad Disks can be removable Drive attached to computer via I/O bus Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, SCSI Host controller in computer uses bus to talk to disk controller built into drive or storage array
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COP 4600: Intro To OS (Mass Storage Systems) Page 3 © Dr. Mark Llewellyn Moving-head Disk Mechanism
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COP 4600: Intro To OS (Mass Storage Systems) Page 4 © Dr. Mark Llewellyn Overview of Mass Storage Structure Magnetic tape Was 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
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COP 4600: Intro To OS (Mass Storage Systems) Page 5 © Dr. Mark Llewellyn Disk Structure Disk drives are addressed as large 1-dimensional arrays of logical blocks , where the logical block is the smallest unit of transfer. The 1-dimensional 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.
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COP 4600: Intro To OS (Mass Storage Systems) Page 6 © Dr. Mark Llewellyn 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 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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This note was uploaded on 10/03/2011 for the course COP 4600 taught by Professor Montagne during the Summer '08 term at University of Central Florida.

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mass storage structures (13) - COP 4600 Summer 2011...

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