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Mass Storage Structure

Mass Storage Structure. Notice: The slides for this lecture have been largely based on those accompanying the textbook Operating Systems Concepts with Java , by Silberschatz, Galvin, and Gagne (2003). Many, if not all, of the illustrations contained in this presentation come from this source.

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Mass Storage Structure

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  1. Mass Storage Structure Notice: The slides for this lecture have been largely based on those accompanying the textbook Operating Systems Concepts with Java, by Silberschatz, Galvin, and Gagne (2003). Many, if not all, of the illustrations contained in this presentation come from this source. CSCI 315 Operating Systems Design

  2. Last Time: Performance I/O a major factor in system performance: • Demands CPU to execute device driver, kernel I/O code. • Context switches due to interrupts. • Data copying. • Network traffic especially stressful. CSCI 315 Operating Systems Design

  3. Intercomputer Communications CSCI 315 Operating Systems Design

  4. Improving Performance • Reduce number of context switches. • Reduce data copying. • Reduce interrupts by using large transfers, smart controllers, polling. • Use DMA. • Balance CPU, memory, bus, and I/O performance for highest throughput. CSCI 315 Operating Systems Design

  5. Device-Functionality Progression CSCI 315 Operating Systems Design

  6. Disk Structure Points to consider: Sector sizes (number of bits per sector) should be fixed. The density of the magnetic material is constant on the surface of the disk. Size of the sector gets smaller as the radius of the track gets smaller. direction of rotation sector read/write head direction of movement The disk rotates at a constant speed. To find a block, the head is moved to the appropriate track, and then the correct sector is found as the disk rotates. arm track Organization of a disk surface CSCI 315 Operating Systems Design

  7. Disk Structure The disk rotation is given in rotations per minute (RPM). The time to find a track is proportional to the distance the head must travel. The average time to find a sector within a track is roughly half the time for a full rotation. Question: If the time to move from track i to track (i+1) is given by d, assuming that the disk head is at track 0 (all the way out), could you calculate the time to get to sector 4 in track 5? direction of rotation sector read/write head direction of movement arm track Organization of a disk surface CSCI 315 Operating Systems Design

  8. Disk Structure Multi-surface disk A cylinder is the collection of all the same tracks across all the multiple disk surfaces. There is a time associated with turning heads on and off so that a different surface can be accessed. We call this overhead the head-switching time. The time to move the arm to read another cylinder is due to the mechanics of the arm. It is certainly much large than the head-switching time, which is due to electronics only. Question: How should one organize data across multiple surfaces to minimize access overhead? direction of rotation read/write heads cylinder arm direction of movement CSCI 315 Operating Systems Design

  9. Disk Scheduling CSCI 315 Operating Systems Design

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