21_Mass_Storage_IO_I

21_Mass_Storage_IO_I - CSC 4103 - Operating Systems Fall...

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1 CSC 4103 - Operating Systems Fall 2009 Tevfik Ko ! ar Louisiana State University November 10th, 2009 Lecture - XXI Overview of Mass Storage Structure Magnetic disks provide bulk of secondary storage of modern computers Drives rotate at 90 to 300 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 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 Hundreds of GB typical storage Common technologies are 4mm, 8mm, 19mm, LTO-2 and SDLT Hierarchical Storage Management (HSM) • A hierarchical storage system extends the storage hierarchy beyond primary memory and secondary storage to incorporate tertiary storage — usually implemented as a jukebox of tapes or removable disks. • Usually incorporate tertiary storage by extending the
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21_Mass_Storage_IO_I - CSC 4103 - Operating Systems Fall...

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