ch12 - Chapter 12 Mass-Storage Systems Silberschatz Galvin...

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Silberschatz, Galvin and Gagne ©2009 Chapter 12: Mass-Storage Systems
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12.2 Silberschatz, Galvin and Gagne ©2009 Chapter 12: Mass-Storage Systems Overview of Mass Storage Structure Disk Structure Disk Attachment Disk Scheduling Disk Management Swap-Space Management RAID Structure Disk Attachment Stable-Storage Implementation Tertiary Storage Devices Operating System Issues Performance Issues
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12.3 Silberschatz, Galvin and Gagne ©2009 Objectives Describe the physical structure of secondary and tertiary storage devices and the resulting effects on the uses of the devices Explain the performance characteristics of mass-storage devices Discuss operating-system services provided for mass storage, including RAID and HSM
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12.4 Silberschatz, Galvin and Gagne ©2009 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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12.5 Silberschatz, Galvin and Gagne ©2009 Moving-head Disk Mechanism
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12.6 Silberschatz, Galvin and Gagne ©2009 Overview of Mass Storage Structure (Cont.) 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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12.7 Silberschatz, Galvin and Gagne ©2009 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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12.8 Silberschatz, Galvin and Gagne ©2009 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
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ch12 - Chapter 12 Mass-Storage Systems Silberschatz Galvin...

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