Download VIII. Input/Output I/O Hardware

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VIII.
Input/Output
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Date
20.04.
27.04.
04.05.
11.05.
18.05.
25.05.
01.06.
08.06.
15.06.
22.06.
29.06.
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12.10.
Lecture
Introduction to Operating Systems
Systems Programming using C (File Subsystem)
Systems Programming using C (Process Control)
Process Scheduling
Process Synchronization
Inter Process Communication
Pfingstmontag
Deadlocks
Memory Management
Hand out
Submission
Course registration
1. Assignment
2. Assignment
1. Assignment
3. Assignment
2. Assignment
4. Assignment
3. Assignment
5. Assignment
4. Assignment
6. Assignment
5. Assignment
7. Assignment
6. Assignment
8. Assignment
7. Assignment
9. Assignment
8. Assignment
10. Assignment
9. Assignment
10. Assignment
Input / Output
Filesystems
Special subject: XQuery your Filesystem
Wrap up session
First examination date
Second examination date
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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I/O Hardware
Control
Unit
I/O Hardware
Different Peripherals
Mass Storage Devices
Processing
Unit
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Input /
Output
(I/O)
3
Main
Memory
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Glatz ©2005
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I/O Hardware
A Typical PC Bus Structure
 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

Memory-mapped I/O
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Silberschatz, Galvin and Gagne ©2005
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Device I/O Port Locations on PCs (partial)
CPU Device
Interaction
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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CPU
CPU↔Device Interaction by Polling
Device Interaction
 CPU determines state of device by repeatedly checking busy flag.
• Principal Choices
• Programmed I/O (Polling)
• CPU waits (busy wait) for peripheral

... prepares data in data-out register (for write operation)

... sets command register to “write”

... sets command-ready bit
 Once controller sees command-ready bit
• Interrupt-Driven I/O
• Peripheral signals „ready“ to CPU by (hardware) interrupt
• Direct Memory Access (DMA)
... sets busy bit

... sees command=write and reads data-in register

... performs write-I/O

... clears command-ready, error & busy bits

Busy bit
• needs special DMA controller to execute I/O independently from CPU

Error bit
• DMA controller signals „ready“ to CPU via (hardware) interrupt

Command register

Data-in, data-out registers
ja
NB: Sind mehrere Zeich
senden, so wiederholt si
Ablauf für jedes weitere
bereit?
nein
Ende
kap61-3_Ein-Ausgabe.fm
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Interrupt-Driven I/O Cycle
CPU↔Device Interaction by Interrupts
Betriebssysteme
 CPU Interrupt-request line (HW wire)
Checked by CPU after each instruction
1 Zeichen senden
1 Zeichen senden
 Busy-wait cycle to wait for I/O from device

Example © Glatz: Serial I/F
Statusregister lesen
Command-ready bit
Triggered by I/O devices
Beispiel: serielle Schnittstelle



6.2.1 Programmgesteuerte E/A
 Interface
• Steal cycles from CPU to transfer data from/to main memory w/o CPU
interaction
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Erkennen einer Unterbrechungsanforderung
Zwei grundsätzliche Fälle:
(1) Externes Hardware-Signal
(2) Unterbrechung als direkte Folge der Instruktionsausführung
■
CPU-instruction cycle © Glatz
■
 Interrupt handler receives interrupts
Initialisierung
loop
 Maskable to ignore or delay some interrupts
FETCH (Instruktion holen)
EXECUTE (Instruktion ausführen)
 Interrupt vector to dispatch interrupt to correct handler

Based on priorities

Some nonmaskable

Using interrupt vector (and chaining)
INTERRUPT CHECK
kap61-3_Ein-Ausgabe.fm
Folie 9
 Interrupt mechanism can also used for

Exceptions

Virtual memory paging

System calls, ...
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Direct Memory Access
Intel Pentium Processor Event-Vector Table
 Used to avoid programmed I/O (PIO, byte-wise data transfer between
memory and devices) for large data movement
 Requires DMA controller
 Bypasses CPU to transfer data directly between I/O device and memory

During DMA access to memory, CPU cannot access memory (“cycle
stealing”)
 Signals completion by a CPU interrupt
 DMA may be implemented into real or into virtual memory
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Betriebssysteme
6.2.3 Ein-/Ausgabe mittels DMA (Direct Memory Access)
DMA: More details
Six Step Process to Perform DMA Transfer
DMA-Betriebsarten
Cycle Stealing
in Single vs. BlockBlocktransfer
Transfer
Einzeltransfer
DMA-Anforderung
DMA-Anforderung
DMAZyklen
DMAZyklen
Betriebssysteme
ProzessorPrinzipaufbau
eines DMA-Kontrollers
ProzessorZyklen
Beispiel für indirekten Transfer:
Zeit
Zyklen
Zeit
DMA: Direct vs. Indirect Data Transfer
kap61-3_Ein-Ausgabe.fm
(A) Programmierung DMA-Kontr.
Hauptspeicher
DMAKontroller
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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CPU
Peripheriegerät
(B) Direkter Transfer
Hauptspeicher
DMAKontroller
CPU
Peripheriegerät
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
kap61-3_Ein-Ausgabe.fm
Folie 24
(C) Indirekter Transfer
Hauptspeicher
DMAKontroller
CPU
Peripheriegerät
Glatz ©2005
Folie 27
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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
Application
I/O-Interface
 Devices vary in many dimensions

Character-stream or block

Sequential or random-access

Sharable or dedicated

Speed of operation

read-write, read only, or write only
Treiberhierarchie
Betriebssystemteil
© Glatz
Anwenderprozess
Geräteverwaltung (I/O manager)
logischer Treiber
Software
Klassentreiber (class driver)
physischer Treiber
Gerätetreiber (device/port driver)
Peripheriekontroller (interface HW)
Hardware
Gerät (device)
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A Kernel I/O Structure
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Characteristics of I/O Devices
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Block and Character Devices
Network Devices
 Block devices include disk drives

Commands include read, write, seek

Raw I/O or file-system access

Memory-mapped file access possible
 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
 Character devices include keyboards, mice, serial ports
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Commands include get, put
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Libraries layered on top allow line editing
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
 Approaches vary widely (pipes, FIFOs, streams, queues, mailboxes)
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Clocks and Timers
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Blocking and Nonblocking I/O
 Blocking - process suspended until I/O completed
 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

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
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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
Difficult to use

I/O subsystem signals process when I/O completed
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Two I/O Methods
Kernel I/O Subsystem
 Scheduling — which I/O request to serve next?

Some I/O request ordering via per-device queue

Some OSs try fairness
 Buffering — store data in memory while transferring between devices

To cope with device speed mismatch

To cope with device transfer size mismatch
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To maintain “copy semantics”
 Caching — fast memory holding copy of data
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Always just a copy

Key to performance
 Spooling — hold output for a device
Synchronous
Asynchronous

If device can serve only one request at a time, e.g., Printing
 Device reservation — provides exclusive access to a device
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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
System calls for allocation and deallocation

Watch out for deadlock!
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
 I/O a major factor in system performance:

Determine device holding file
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Demands CPU to execute device driver, kernel I/O code
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Translate name to device representation
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Context switches due to interrupts
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Physically read data from disk into buffer

Data copying

Make data available to requesting process

Network traffic especially stressful

Return control to process
Software
Anwenderprozess 1
Anwenderprozess 2
Anwenderprozess n
© Glatz
 Improving Performance:
Hardware
Treiber A
Kontroller A
Gerät A
Treiber B
Kontroller B
Gerät B

Reduce number of context switches

Reduce data copying in memory between application and device

Reduce frequency of interrupts by using large transfers, smart
controllers, polling

Use DMA to increase concurrency (offload CPU)

Move processing into device controllers (offload CPU & bus)

Balance CPU, memory, bus, and I/O performance for highest
throughput
Geräteverwaltung
(I/O manager)
Treiber X
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Performance
Transforming I/O Requests to Hardware Operations
 Consider reading a file from disk for a process:
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Kontroller X
Gerät X
Treiber-Schnittstelle (driver interface)
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Overload
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in one of these will leave others idle!
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Mass Storage Overview
• Secondary Storage
• Magnetic disks provide bulk of secondary storage of modern computers
• Disks can be removable
• Drives attached to computer via I/O bus (e.h., EIDE,ATA, SATA, USB, FC,
SCSI, ...)
Mass Storage
• Host controller (in computer) talks to disk controller (in device) via this
bus
• Tertiary Storage
• Low cost is defining characteristic
• Typically uses removable media
• Considered „off-line“ storage; robot-machinery can turn it into“near-line“
• Magnetic tapes, floppy, CD, DVD, ...
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Moving-head Disk Machanism
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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.
© Glatz
Seite 0
Sektor 8
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Sektor 7
Seite 1
Sektor 1
Zylinder 0
0
Zylinder 1
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Zylinder 2
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Sektor 6
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Disk access time = queue waiting + seek + rotational delay + transfer
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Sektor 5
Sektor 2
Sektor 3
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Sektor 7
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Sektor 6
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Sektor 3
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Sektor 5
Sektor 2
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Sektor 4
Sektor 1
Zylinder 0
Zylinder 1
Zylinder 2
Sektor 8
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Sektor 4
Nummerierung: Zylinder 0.. (zero based), Seiten 0.. (zero based), Sektoren 1.. (one based)
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Disk Attachment
Network-Attached Storage
 Network-attached storage (NAS) is storage made available over a
 Host-attached storage accessed through I/O ports talking to I/O busses
network rather than over a local connection (such as a bus)
 SCSI itself is a bus, up to 16 devices on one cable, SCSI initiator
 NFS and CIFS are common protocols
requests operation and SCSI targets perform tasks

 Implemented via remote procedure calls (RPCs) between host and
Each target can have up to 8 logical units (disks attached to device
controller
storage
 New iSCSI protocol uses IP network to carry the SCSI protocol
 FC is high-speed serial architecture

Can be switched fabric with 24-bit address space – the basis of
storage area networks (SANs) in which many hosts attach to many
storage units

Can be arbitrated loop (FC-AL) of 126 devices
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Storage Area Network
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Disk Management
 Common in large storage environments (and becoming more common)
 Low-level formatting, or physical formatting — Dividing a disk into sectors
that the disk controller can read and write.
 Multiple hosts attached to multiple storage arrays - flexible
 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.
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Logical formatting or “making a file system”.
 Boot block initializes system.

The bootstrap is stored in ROM.

Bootstrap loader program.
 Methods such as sector sparing used to handle bad blocks.
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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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
Disk Scheduling

Seek time is the time for the disk are 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 Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Disk Scheduling (Cont.)
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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FCFS — First Come First Served
Illustration shows total head movement of 640 cylinders.
 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 Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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SSTF — Shortest Seek Time First
SCAN (aka. Elevator Algorithm)
 Selects the request with the minimum seek time from the current head
 The disk arm starts at one end of the disk, and moves toward the other
position.
end, servicing requests until it gets to the other end of the disk, where the
head movement is reversed and servicing continues.
 SSTF scheduling is a form of SJF scheduling; may cause starvation of
 Illustration shows total head movement of 208 cylinders.
some requests.
 Illustration shows total head movement of 236 cylinders.
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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C-SCAN
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C-LOOK
 Provides a more uniform wait time than SCAN.
 Somewhat smarter version of C-SCAN
 The head moves from one end of the disk to the other, servicing requests
 Arm only goes as far as the last request in each direction, then reverses
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.
direction immediately, without first going all the way to the end of the
disk.
 Treats the cylinders as a circular list that wraps around from the last
cylinder to the first one. (→“Circular Scan”)
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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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.
RAID-Systems
(Disk Arrays)
 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.
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RAID Levels
RAID-Systems — Basic Ideas
• Idea came up in the 1980s
 Large variety of exact definitions of the
• „Winchester disk drives“: smaller, cheaper, less power & space/
volume consumption, no air conditioning, ...
than state-of-the-art mainframe disk drives
• But: Many disk drives largely reduced MTTF (by factor 1/n, assuming independence)
levels, plus additional levels.
 Various choices as to how and where to
implement RAID functionality (OS, drive,
controller, SAN interconnect; HW/SW;...)
 Additional functionality can be
integrated, such as replication and
snapshots.
• Need to use redundancy to improve/regain reliability
• Many disks can also provide much better performance
• Can also avoid restrictions of file systems:
 Volume mgmt. software offers a lot of
additional functionality.
 Hot spare disks can be reserved as
• files must fit onto single disk → „logical volumes“ spanning disks
„immediate“ replacement.
• Striping: use a group of disks as a single storage unit
• Mirroring/Shadowing or Parity/ECCs improve reliability by
storing redundant data
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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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 file system.
More Aspects
 Automatically migrate data up and down the storage hierarchy

Small and frequently used files remain on disk.

Large, old, inactive files are archived to the jukebox.
 HSM is usually found in supercomputing centers and other large
installations that have enormous volumes of data.
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Cost
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Price per Megabyte of DRAM (1981 to 2004)
 Main memory is much more expensive than disk storage
 The cost per megabyte of hard disk storage is competitive with magnetic
tape if only one tape is used per drive.
 The cheapest tape drives and the cheapest disk drives have had about
the same storage capacity over the years.
 Tertiary storage gives a cost savings only when the number of cartridges
is considerably larger than the number of drives.
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Price per Megabyte of Magnetic Hard Disk (1981 to 2004)
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Price per Megabyte of a Tape Drive (1984-2000)
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Intended Schedule
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✏
Date
20.04.
27.04.
04.05.
11.05.
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25.05.
01.06.
08.06.
15.06.
22.06.
29.06.
06.07.
13.07.
20.07.
27.07.
12.10.
Lecture
Introduction to Operating Systems
Systems Programming using C (File Subsystem)
Systems Programming using C (Process Control)
Process Scheduling
Process Synchronization
Inter Process Communication
Pfingstmontag
Deadlocks
Memory Management
Hand out
Submission
Course registration
1. Assignment
2. Assignment
1. Assignment
3. Assignment
2. Assignment
4. Assignment
3. Assignment
5. Assignment
4. Assignment
6. Assignment
5. Assignment
7. Assignment
6. Assignment
8. Assignment
7. Assignment
9. Assignment
8. Assignment
10. Assignment
9. Assignment
10. Assignment
IX.
File Systems
Input / Output
Filesystems
Special subject: XQuery your Filesystem
Wrap up session
First examination date
Second examination date
Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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Operating Systems • Prof. Dr. Marc H. Scholl • DBIS • U KN • Summer Term 2009
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