Windows 2000 I/O System, Cache Manager and File Systems

1
Windows 2000 I/O System, Cache Manager and File
Systems

• Computing Department,
• Lancaster University, UK

2
Overview

• Goals
• Overview of I/O System
• Overview of Cache Manager
• Overview of File Systems

3
I/O System

• Design goals
• Make I/O processing fast on both single and
  multiprocessor systems
• Protect shareable resources by using standard
  Windows 2000 security mechanisms
• Meet requirements for the various sub-systems
  available
• Provide services to make device driver
  development as easy as possible
• Allow device drivers to be added or removed
  dynamically
• Provide support for multiple installable file
  systems

4
I/O System Components (1)

• The I/O manager
• Connects applications and system components to
  virtual, logical and physical devices
• A device driver
• Typically provides an I/O interface for a
  particular type of device
• The PnP manager
• Responsible for loading a device driver when a
  device is detected
• The power manager
• Guides the system through power-state transitions

5
I/O System Components (2)

• The registry
• Serves as a database that stores a description of
  basic hardware devices attached to the system
• INF files
• Driver installation files
• The link between a particular device, and the
  driver that assumes its primary control
• Hardware Abstraction Layer (HAL)
• Insulates the drivers from the specifics of the
  processor and interrupt controller
• Provides APIs that hide the differences between
  platforms

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I/O Operations

• Most I/O operations dont involve all components
• Typical request starts with an app executing an
  I/O related function, that is processed by the
  I/O manager, one or more device drivers and the
  HAL
• The OS abstracts all I/O requests as operations
  on a virtual file
• Hiding the fact that the target might not be a
  file-structured device
• Abstraction generalises an applications
  interface to devices
• All data that is read or written is regarded as a
  simple stream of bytes directed to these files
• The I/O manager dynamically directs these virtual
  file requests to the appropriate device driver

7
Flow of a Typical I/O Request
User-mode API
I/O Subsystem API
I/O Manager
Driver support routines
Kernel mode device drivers
HAL I/O access routines
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Types of Device Drivers

• File system drivers
• Accept I/O requests to files
• Windows 2000 drivers
• Include drivers for mass storage devices, net.
  adaptors
• Legacy drivers
• Written for NT
• Display drivers
• Translate device-independent graphics requests to
  device-specific requests
• WDM drivers (Windows Driver Model)
• Includes support for power management, PnP, etc

9
User-mode Drivers

• Virtual device drivers (VDDs)
• Used to emulate 16-bit MS-DOS applications
• Printer drivers
• Translate device-independent graphics requests to
  printer-specific commands

10
Win32 Input/Output APIs

• A few device-independent APIs available
• CreateFile
• ReadFile / WriteFile
• CloseHandle
• Many (over 100) device-type-dependent APIs
• disk
• tape
• console
• pipes
• sound cards
• etc

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Device and File Naming

• File names
• \\.\disk\directory\\file
• \\server\disk\directory\\file
• Local device names
• \\.\name-of-device
• Remote device names Universal Name Convention
• \\server\name-of-shared-resource
• DOS-style built-in device names for compatibility
• A, B, D etc
• Windows 2000 internal name differ from externally
  visible names

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Overview of Cache Manager

• What is the cache manager?
• A set of kernel-mode functions and system
  threads that cooperate with the memory manager to
  provide data caching for all Windows 2000 file
  system drivers
• Most OSs rely on each individual file system to
  cache data
• Duplicate caching / memory management code
• Limitations on the kinds of data that can be
  cached
• Windows 2000 facilitates the caching of all
  externally stored data
• Whether on local hard disks, floppy disks,
  network file servers, CD-ROMs
• Any kind of data can be cached
• User data streams (the contents of a file,
  on-going r/w)
• File system metadata (e.g. directory and file
  headers)

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Cache Manager Key Features

• Supports all file system types
• Removes the need for each file system to
  implement its own cache management code
• Uses the memory manager to control what parts of
  the files are in physical memory (see next slide)
• Allowing a trade-off for physical memory between
  user processes and the OS
• Caches data on a virtual block basis
• In contrast to most caching systems, which cache
  on a logical block basis
• ? provides fast I/O intelligent read-ahead and
  high-speed access to the cache without involving
  file-system drivers

14
Interaction Between the Cache and the Memory
Manager

• Unusual aspect Cache manager never actually
  knows how much cached data is in physical memory!
• This is because it maps views of files into
  system virtual address spaces
• The memory manager then pages in blocks that
  arent in physical memory, and pages data out
  too
• The approach avoids the cache manager generating
  read or write I/O request packets to access the
  data for files its caching
• Instead, it copies data from the virtual address
  of where the portion of the file is, and relies
  on the memory manager to fault in the data, if
  needed

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Overview of File Systems

• NTFS native file system format for Win2000
• Also includes support for
• CDFS
• UDF
• FAT12, FAT16 and FAT32

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CDFS File System

• CD-ROM file system simple format defined in
  1998 as the read-only formatting standard for CD
• Format has a number of restrictions
• Directory and file names must be fewer than 32
  characters long
• Directory trees can be no more than eight levels
  deep
• Now considered legacy. because of

17
UDF File System

• Format replacing CDFS for optical storage media
• DVD-ROM in mind
• Designed with rewritable media in mind, Windows
  2000 UDF driver only provides read-only support
• File systems have the following features
• Filenames can be 255 characters long
• Maximum path length is 1023 characters
• Filenames can be upper and lower case

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FAT12, FAT16 and FAT32

• Supported to enable upgrades from other versions
  of Windows, and for compatibility with other
  OSs, and for use as a floppy disk format
• 12, 16 and 32 represent the number of bits the
  format uses to identify clusters on a disk
• Windows 2000 uses cluster sizes of 512 bytes to 8
  KB in size, limiting a FAT12 volume to 32MB
• Windows 2000 uses FAT12 as the format for floppy
  disks
• FAT32 (most recently defined)
• Used in Win95 (OSR2), Win98 and Win Millennium

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NTFS

• Uses 64-bit cluster indexes
• NTFS has the ability to address volumes up to 16
  exabytes (16 million GB)
• Windows 2000 limits the size of an NTFS volume to
  that addressable using 32-bit clusters
• 128 TB (using 64KB clusters)

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NTFS Advanced Features (1)

• Recoverability
• File system structures can be repaired to a
  consistent state (no loss of file or directory
  structure info file data can be lost)
• File and directory security
• Files and directories are protected from
  unauthorised access using a combination of a
  security ID (stored as part of the file) and the
  password entered
• File compression
• Transparent to application
• Directory compression also possible

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NTFS Advanced Features (2)

• Disk quotas
• Per-user volume quotas
• NTFS tags files and directories with the security
  ID of the user who created them
• Encryption
• Supports EFS Encrypting File System
• Transparent to application
• Files are accessed using using the private key of
  an accounts EFS private / public key pair
• etc