Slide #1.

Chapter 12: Mass-Storage Systems Operating System Concepts with Java – 8th Edition 12.1 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #2.

Chapter 12: Mass-Storage Systems  Overview of Mass Storage Structure  Disk Structure  Disk Attachment  Disk Scheduling  Disk Management  RAID Structure Operating System Concepts with Java – 8th Edition 12.2 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #3.

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 Operating System Concepts with Java – 8th Edition 12.3 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #4.

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 Operating System Concepts with Java – 8th Edition 12.4 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #5.

Moving-head Disk Mechanism Operating System Concepts with Java – 8th Edition 12.5 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #6.

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 Operating System Concepts with Java – 8th Edition 12.6 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #7.

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 Operating System Concepts with Java – 8th Edition 12.7 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #8.

Disk Scheduling  The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth  Access time has two major components  Seek time is the time for the disk to move the heads to the cylinder containing the desired sector  Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head  Minimize seek time  Seek time  seek distance  Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer Operating System Concepts with Java – 8th Edition 12.8 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #9.

Disk Scheduling (Cont)  Several algorithms exist to schedule the servicing of disk I/O requests  We illustrate them with a request queue (0-199) 98, 183, 37, 122, 14, 124, 65, 67 Head pointer 53 Operating System Concepts with Java – 8th Edition 12.9 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #10.

First-come, first-served (FCFS) Illustration shows total head movement of 640 cylinders Operating System Concepts with Java – 8th Edition 12.10 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #11.

Shortest seek time first (SSTF)  Selects the request with the minimum seek time from the current head position  SSTF scheduling is a form of SJF scheduling; may cause starvation of some requests  Illustration shows total head movement of 236 cylinders Operating System Concepts with Java – 8th Edition 12.11 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #12.

SCAN  The disk arm starts at one end of the disk, and moves toward the other end, servicing requests until it gets to the other end of the disk, where the head movement is reversed and servicing continues.  SCAN algorithm Sometimes called the elevator algorithm  Illustration shows total head movement of 208 cylinders Operating System Concepts with Java – 8th Edition 12.12 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #13.

SCAN (Cont.) Operating System Concepts with Java – 8th Edition 12.13 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #14.

C-SCAN  Provides a more uniform wait time than SCAN  The head moves from one end of the disk to the other, servicing requests as it goes  When it reaches the other end, however, it immediately returns to the beginning of the disk, without servicing any requests on the return trip  Treats the cylinders as a circular list that wraps around from the last cylinder to the first one Operating System Concepts with Java – 8th Edition 12.14 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #15.

C-SCAN (Cont) Operating System Concepts with Java – 8th Edition 12.15 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #16.

C-LOOK  Version of C-SCAN  Arm only goes as far as the last request in each direction, then reverses direction immediately, without first going all the way to the end of the disk Operating System Concepts with Java – 8th Edition 12.16 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #17.

Selecting a Disk-Scheduling Algorithm  SSTF is common and has a natural appeal  SCAN and C-SCAN perform better for systems that place a heavy load on the disk  Performance depends on the number and types of requests  Requests for disk service can be influenced by the file- allocation method  The disk-scheduling algorithm should be written as a separate module of the operating system, allowing it to be replaced with a different algorithm if necessary  Either SSTF or LOOK is a reasonable choice for the default algorithm Operating System Concepts with Java – 8th Edition 12.17 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #18.

Disk Management  Low-level formatting, or physical formatting — Dividing a disk into sectors that the disk controller can read and write  To use a disk to hold files, the operating system still needs to record its own data structures on the disk  Partition the disk into one or more groups of cylinders  Logical formatting or “making a file system”  To increase efficiency most file systems group blocks into clusters  Disk I/O done in blocks  File I/O done in clusters  Boot block initializes system  The bootstrap is stored in ROM  Bootstrap loader program  Methods such as sector sparing used to handle bad blocks Operating System Concepts with Java – 8th Edition 12.18 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #19.

Booting from a Disk in Windows 2000 Windows 2000 places its boot code in the first sector on the hard disk (master boot record). Disk divided into more than one partitions with one as boot partition, which contains OS and device drivers. Operating System Concepts with Java – 8th Edition 12.19 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #20.

RAID Structure  RAID – multiple disk drives provides reliability via redundancy  Increases the mean time to failure  Frequently combined with nonvolatile RAM (NVRAM) to cache the RAID array. This write-back cache is protected from data loss during power failures.  RAID is arranged into six different levels Operating System Concepts with Java – 8th Edition 12.20 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #21.

RAID (Cont)  Several improvements in disk-use techniques involve the use of multiple disks working cooperatively  Disk striping uses a group of disks as one storage unit  RAID schemes improve performance and improve the reliability of the storage system by storing redundant data  Mirroring or shadowing (RAID 1) keeps duplicate of each disk  Striped mirrors (RAID 1+0) or mirrored stripes (RAID 0+1) provides high performance and high reliability  Block interleaved parity (RAID 4, 5, 6) uses much less redundancy  RAID within a storage array can still fail if the array fails, so automatic replication of the data between arrays is common Operating System Concepts with Java – 8th Edition 12.21 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #22.

RAID Levels Operating System Concepts with Java – 8th Edition 12.22 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #23.

RAID (0 + 1) and (1 + 0) Operating System Concepts with Java – 8th Edition 12.23 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #24.

Chapter 13: I/O Systems  I/O Hardware  Application I/O Interface  Kernel I/O Subsystem  Transforming I/O Requests to Hardware Operations Operating System Concepts with Java – 8th Edition 12.24 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #25.

I/O Hardware  Incredible variety of I/O devices  Common concepts  Port  Bus (daisy chain or shared direct access)  Controller (host adapter)  I/O instructions control devices  Devices have addresses, used by  Direct I/O instructions (the controller has one or more registers for data and control signals).  Memory-mapped I/O (device control registers are mapped into the address space of the processor). Operating System Concepts with Java – 8th Edition 12.25 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #26.

A Typical PC Bus Structure Operating System Concepts with Java – 8th Edition 12.26 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #27.

Device I/O Port Locations on PCs (partial) Operating System Concepts with Java – 8th Edition 12.27 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #28.

Polling  Determines state of device command-ready busy Error  Busy-wait cycle to wait for I/O from device Operating System Concepts with Java – 8th Edition 12.28 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #29.

Interrupts  CPU Interrupt-request line (a wired in CPU hardware) triggered by I/O device  When the CPU detects that a controller has asserted a signal on the interrupt-request line, the CPU performs a state save and jump to the interrupt-handler routine at a fixed address in memory.  Maskable to ignore or delay some interrupts when CPU is executing something critical  Interrupt vector to dispatch interrupt to correct handler  Based on priority  Some nonmaskable  Interrupt mechanism also used for exceptions Operating System Concepts with Java – 8th Edition 12.29 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #30.

Interrupt-Driven I/O Cycle Operating System Concepts with Java – 8th Edition 12.30 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #31.

Intel Pentium Processor Event-Vector Table Operating System Concepts with Java – 8th Edition 12.31 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #32.

Direct Memory Access  Used to avoid programmed I/O for large data movement  Requires DMA controller  Bypasses CPU to transfer data directly between I/O device and memory Operating System Concepts with Java – 8th Edition 12.32 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #33.

Six Step Process to Perform DMA Transfer Operating System Concepts with Java – 8th Edition 12.33 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #34.

Application I/O Interface  I/O system calls encapsulate device behaviors in generic classes  Device-driver layer hides differences among I/O controllers from kernel  Devices vary in many dimensions  Character-stream  Sequential  Sharable  Speed or block or random-access or dedicated of operation  read-write, read only, or write only Operating System Concepts with Java – 8th Edition 12.34 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #35.

A Kernel I/O Structure Operating System Concepts with Java – 8th Edition 12.35 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #36.

Characteristics of I/O Devices Operating System Concepts with Java – 8th Edition 12.36 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #37.

Block and Character Devices  Block devices include disk drives  Commands  Raw include read, write, seek I/O or file-system access  Memory-mapped file access possible  Character devices include keyboards, mice, serial ports  Commands  Libraries include get(), put() layered on top allow line editing Operating System Concepts with Java – 8th Edition 12.37 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #38.

Network Devices  Varying enough from block and character to have own interface  Unix and Windows NT/9x/2000 include socket interface  Separates network protocol from network operation  Includes select() functionality  Approaches vary widely (pipes, FIFOs, streams, queues, mailboxes) Operating System Concepts with Java – 8th Edition 12.38 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #39.

Clocks and Timers  Provide current time, elapsed time, timer  Programmable interval timer used for timings, periodic interrupts  ioctl() (on UNIX) covers odd aspects of I/O such as clocks and timers Operating System Concepts with Java – 8th Edition 12.39 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #40.

Blocking and Nonblocking I/O  Blocking - process suspended until I/O completed  Easy to use and understand  Insufficient for some needs  Nonblocking - I/O call returns as much as available  User interface, data copy (buffered I/O)  Implemented via multi-threading  Returns quickly with count of bytes read or written  Asynchronous - process runs while I/O executes  Difficult to use  I/O subsystem signals process when I/O completed Operating System Concepts with Java – 8th Edition 12.40 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #41.

Two I/O Methods Asynchronous Synchronous Operating System Concepts with Java – 8th Edition 12.41 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #42.

Device-status Table Operating System Concepts with Java – 8th Edition 12.42 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #43.

Sun Enterprise 6000 Device-Transfer Rates Operating System Concepts with Java – 8th Edition 12.43 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #44.

Kernel I/O Subsystem  Caching - fast memory holding copy of data  Always just a copy  Key to performance  Spooling - hold output for a device  If device can serve only one request at a time  i.e., Printing  Device reservation - provides exclusive access to a device  System calls for allocation and deallocation  Watch out for deadlock Operating System Concepts with Java – 8th Edition 12.44 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #45.

Error Handling  OS can recover from disk read, device unavailable, transient write failures  Most return an error number or code when I/O request fails  System error logs hold problem reports Operating System Concepts with Java – 8th Edition 12.45 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #46.

I/O Protection  User process may accidentally or purposefully attempt to disrupt normal operation via illegal I/O instructions All I/O instructions defined to be privileged I/O must be performed via system calls  Memory-mapped and I/O port memory locations must be protected too Operating System Concepts with Java – 8th Edition 12.46 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #47.

Use of a System Call to Perform I/O Operating System Concepts with Java – 8th Edition 12.47 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #48.

Kernel Data Structures  Kernel keeps state info for I/O components, including open file tables, network connections, character device state  Many, many complex data structures to track buffers, memory allocation, “dirty” blocks  Some use object-oriented methods and message passing to implement I/O Operating System Concepts with Java – 8th Edition 12.48 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #49.

UNIX I/O Kernel Structure Operating System Concepts with Java – 8th Edition 12.49 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #50.

I/O Requests to Hardware Operations  Consider reading a file from disk for a process: Determine Translate name to device representation Physically Make device holding file read data from disk into buffer data available to requesting process Return control to process Operating System Concepts with Java – 8th Edition 12.50 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #51.

Life Cycle of An I/O Request Operating System Concepts with Java – 8th Edition 12.51 Silberschatz, Galvin and Gagne ©2009
More slides like this


Slide #52.

End of Chapter 13 Operating System Concepts with Java – 8th Edition 12.52 Silberschatz, Galvin and Gagne ©2009
More slides like this