Transcript 9781111543709 _PPT_ch05

Guide to Parallel Operating
Systems with
Windows 7 and Linux
Chapter 5
File Systems
Objectives
• Describe the characteristics of three Windows 7 file
systems
• Describe the characteristics of four Fedora 13 file
systems
• Create a file system in Windows 7 and Fedora 13
• Mount a file system in Windows 7 and Fedora 13
• Manage file systems in Windows 7 and Fedora 13
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Windows 7 File System
Characteristics
• To implement a file system, you need to know the
following:
– Allocation of the storage areas on the hard drive
– Assignment of drive letters:
• Used to access storage areas
– Characteristics of available file systems
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Disk Partitions
• Figure 5-1:
– Shows BIOS settings for three SATA-controlled
drives
– Each SATA drive has its own disk controller
– CD-ROM drive has its own controller
• Figure 5-2:
– Each controller supports one device that could be a
hard drive or CD-ROM drive
• Figure 5-3: shows drives separated into partitions
• Types of storage in Windows 7:
– Basic and dynamic
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Figure 5-1 BIOS settings for SATA-controlled drives in Virtual PC 2007
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Figure 5-2 Sample devices for SATA-controlled drives
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Figure 5-3 Partitions on three hard drives and a CD-ROM drive
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Disk Partitions (continued)
• Primary partition features:
– Normally contains an OS, such as Windows 7
– Physical hard drive can have four primary partitions
• Limit drops to three if extended partitions are used
• Only one extended partition can be allocated per
physical hard drive
– However, multiple logical drives can be allocated
within an extended partition
• Volume:
– A fixed amount of storage on a hard drive
• Hard drive can be initialized as a dynamic disk
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Drive-Lettering Conventions
• Windows 7:
– Follows drive-lettering conventions
– Assigns a letter to each hard drive and optical drive
• Creating partitions and logical drives for Figure 5-4:
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System Reserved partition: no drive letter
First primary partition on disk 0 assigned drive letter C
CD-ROM drive received drive letter D
Disk 1 received drive letter E
Disk 2 received drive letter F
• View assignments with Disk Management console
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Figure 5-4 Disk Manager showing drive letters after additions
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FAT16 File System
• FAT (File Allocation Table): file system for early PCs
– Supported by Windows 7 and Linux
• FAT16 disk hierarchy:
– Sector: smallest unit of space, usually 512 bytes
– Cluster: group of sectors
• Size is related to the size of the disk partition
• Size range: 4 sectors to 64 sectors
• FAT12:
– Predecessor to FAT16
– Counter for the cluster address was limited to 12 bits
– Used on first 10-MB hard drives in the IBM PC XT
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FAT16 File System (continued)
• Subdirectories: logical grouping of related files
• FAT 16 permits partitions of up to 2 GB
• Partition size:
– Limited by the 8-bit count of sectors per cluster
• In Windows 7:
– The length of a filename may be 256 characters
– Filenames are case insensitive
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FAT16 File System (continued)
Table 5-1 Cluster sizes
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FAT32 File System
• Uses 32-bit cluster numbers (28 bits currently used)
• Continues use of subdirectories and long filenames
• Theoretical size limits:
– 268,435,438 cluster based on 28-bit cluster address
– Drive sizes of approximately 2 terabytes (trillion bytes)
• For Windows 7:
– Partition limit is 32 GB for the primary partition
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NT File System
• Default file system for new installations of Windows 7
• NTFS (New Technology File System) features:
– Supports volumes as large as 2 terabytes
– Cluster sizes: 512 bytes to 64 KB (4 KB default)
– Master file table (MFT): used to manage NTFS volume
• Allocates space for each file record
• File attributes written to allocated space in MFT
• Binary search algorithm used to locate items
• Options unique to NTFS: journalizing, compression,
encryption, security, auditing, and quotas
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Journalizing ̶ Ensuring that Data is
Written
• Maintains data integrity for the hard drive
• How NTFS provides a fail-safe file system:
– Corrects itself against a hard drive sector corruption
– Protects against power loss during hard drive writes
• NTFS uses transactions:
– Write action is either accomplished or canceled
• Scenario 1: sector damaged during write operation
– Response: sector marked; data written to good sector
• Scenario 2: power is lost during write operation
– Response: transaction processed after OS restarts
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Compression ̶ Saving Space
• Compression technology reduces file sizes:
– Example: word-processing documents compress well
• Access compressed files with decompression:
– Recompress files before rewriting to hard drive
• Performance considerations:
– Decompression/recompression requires CPU cycles
• System performance may be adversely affected
– Reserve compression for little used files and folders
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Encryption ̶ Protecting Data
• Effects of applying NTFS encryption to a file:
– Only the file creator can view file contents
– Non-authorized user will not see meaningful data
– File decrypted when accessed by an application
• Administrator can decrypt file in emergency
• A file can be encrypted or compressed, but not
both
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Security ̶ Restricting Access
• Windows 7:
– Controls access to files and folders
– Designed to provide security for files and folders
accessed on an NTFS
• Three elements required for file access:
– User account
– User password
– Permissions
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Auditing ̶ Tracking Access
• Auditing not “turned on” by default:
– Significant processing resources required
• With auditing enabled:
– Windows 7 can be configured to keep track of
events
– Event occurrence causes entry in security log
• Information about access events include:
– Type of event, date and time the event occurred
– Which user triggered the event
• Security log may only be viewed by authorized user
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Quotas ̶ Limiting Storage
• Storage quotas set for individuals and storage areas:
– Implemented in Windows 7 when a PC is shared
– Administrator cannot limit space for a group
• Consequence of storing data beyond quota:
– User receives message indicating hard drive is full
• Log file stores information regarding quotas:
– Used to determine which users are at or near quota
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Optical Media File Systems
• Optical disc: storage medium manipulated with lights
• Windows 7 supports two file systems for optical
media:
– UDF (Universal Disk Format):
• Read-write interoperable among major OSs
• Compatible between rewritable and write-once media
• Implementations: DVDs, CD-Rs, and CD-RWs
– Compact Disc File System (CDFS):
• Alias for ISO 9660 (CD-ROM file system standard)
• Makes CD-ROMs readable by many different platforms
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Fedora 13 File System Characteristics
• File system knowledge areas to master:
– Allocation of the partitions on the hard drive
• Each partition on a physical drive is named
– Creation of file systems on the partitions
• Partition is formatted for the type of file system
• File systems are mounted on mount points
– Creation and management of directories and files
– Characteristics of available file systems
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Disk Partitions
• Disks on the Fedora 13 virtual machine:
– Allocated to mimic drives on the Windows 7 virtual
machine
• Windows 7 disks (Disk 0, Disk 1, and Disk 2):
– Match up with Fedora 13 disks (sda, sdb, and sdc)
– Operating systems:
• Installed on the first virtual disk (Disk 0 or sda)
– Partitions:
• The same on the remaining two virtual disks
• Fedora 13: assigns partitions on a hard drive
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Figure 5-5 Fedora 13 partitions on three disks and a CD-ROM drive
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Disk Partitions (continued)
Table 5-2 Mimicked drives
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Drive Partition Naming Conventions
• Partition name: device name and partition number
• Physical drives allocated one or more partitions:
– First SATA drive is called sda, the second sdb, etc.
– Example:
• Fedora 13 is usually installed on first physical hard
drive (sda1)
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File Systems in Fedora 13
• Extended 2 file system (ext2fs):
– Most widely used file system in Fedora 13
• Ext2fs provides the same functionality as NTFS:
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Compression: reduces file storage space
Encryption: protects files from intruders
Security: restricts access to authorized users
Auditing: tracks file access (actual or attempted)
Quotas: limits total size of files per user
• Some other file systems used in Fedora 13:
– ext3fs: implements journalizing
– NTFS: read-only access is provided
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File System Creation
• Formatting:
– Prepares a storage area for use
– Creates root of directory structure and file system
• Tools for creating a storage area and a file system:
– Windows 7: uses the Disk Management console
– Linux: uses the fdisk and mkfs programs
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Windows 7 File System Creation
• Chief tool: Disk Management console
• When creating storage area:
– Start with an unallocated area on a physical disk
– New Simple Volume wizard: used to start process
• Options in the Assign Drive Letter/Path dialog box:
– Assign the following drive letter
– Mount in the following empty NTFS folder
– Do not assign a drive letter or drive path
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Figure 5-7 Specifying a partition size
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Figure 5-8 Assigning a drive letter
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Windows 7 File System Creation
(continued)
• You must format the partition before you can use it
• Format Partition dialog box
• You can configure a number of options:
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Do not format this volume
Format this volume with the following settings
File system
Allocation unit size
Volume label
Perform a quick format
Enable file and folder compression
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Figure 5-9 Format Partition options
Courtesy Course Technology/Cengage Learning
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Fedora 13 File System Creation
• Used for storing system configurations and data
• Initial structure created: “/” directory and swap file
• Uses for the hidden swap file:
– Holding parts of programs and data files
– OS moves data between swap file and memory
• Define file systems after “/” and swap file:
– Create a new partition using the fdisk command
– Create the file system using the mkfs command
• Example: mkfs -t ext2 /dev/fd0
– If mount point needed, use mkdir to create a directory
• Example: mkdir /home/User01/mydirectory
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Table 5-3 Fedora 13 default directories
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Mounting a File System
• Windows 7’s approach to mounting a file system:
– Letters given to partitions, volumes, CD-ROM drives
– “Premounted” storage items available at any time
– Performance is traded for user convenience
• Fedora 13’s approach to mounting a file system:
– Mount file systems as they are needed
– User convenience is traded for performance
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Mounting a Windows 7 File System
• Removable drives:
– Mounted upon insertion into USB port
– Prior to removal, you must notify Windows 7
– Data transfer: may be interrupted if USB drive
removed too soon
• Mounted drive:
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Supported by Windows 7 and Fedora 13
Mapped to empty folder on a volume that uses NTFS
Assigned drive path instead of drive letter
Adds flexibility to storage management
To access: click drive icon
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Mounting a Fedora 13 File System
• Mounting: makes a file system available for use
– After mounting, files are accessible at mount point
– Superuser access required to mount a file system
• Some partitions are mounted automatically:
– Script in /etc/rc.d executes mount -a command
– File systems in /etc/fstab (except noauto) mounted
• mount attaches file system to partition via mount
point:
– /mnt directory is a generic mount point
– Command syntax:
mount -t type device mount-point
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Figure 5-12 Displaying mounted file systems in Fedora 13
Courtesy Course Technology/Cengage Learning
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Figure 5-13 Mounting a file system in Fedora 13
Courtesy Course Technology/Cengage Learning
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Managing File Systems
• Windows 7:
– Local Disk Properties dialog box assists in file
management
• Fedora 13:
– Use fsck command to manage the swap space
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Managing Windows 7 File Systems
• General tab manages disk space:
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Type: a local disk is a hard drive on the PC
File system: indicates the file system type on the drive
Used space: displays amount of used space on drive
Free space: displays amount of unused space on
drive
Capacity: displays the total capacity of the disk drive
Disk Cleanup: removes temporary and Internet files
Compress drive to save disk space
Allow files on this drive to have contents indexed in
addition to file properties
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Tools Tab
• Provides three disk-tuning tools
• Error-checking:
– Scans the volume for damage
– Volume is not available during the scan
• Defragmentation:
– Analyzes drives for fragmentation (scattered files)
– Tool: analyzes and reorganizes drives
• Backup:
– Copies contents of files and folders
– Option not available on Windows 7 Home edition
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Hardware Tab
• Provides access to drive information and settings
• Options to view information:
– Name and Type: display drive’s model names and
types
– Properties button: provides access to the Properties
dialog box for a selected device
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Sharing Tab
• Shares the entire contents of a drive
• Hidden share C$ is displayed in dialog box
(default)
• Creating additional shares (for administrators):
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Click the New Share button
Type the share name in the Share name text box
Click the Permissions button
Check the appropriate Allow check boxes
Click OK twice
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Security Tab
• Used to set the NTFS permissions:
– NTFS permissions control access to data on drive
• Modifying NTFS group permissions (administrator):
– Set the Allow check boxes for each user group
– Click OK
– You will be prompted for an administrative account
password
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Quota Tab
• Tracks/controls disk space usage for NTFS volumes
• Used by administrators to optimize use of disk space
• Options:
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Enable quota management
Deny disk space to users exceeding quota limit
Do not limit disk usage
Limit disk space to
Set warning level to
Log event when a user exceeds their quota limit
Log event when a user exceeds their warning level
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Managing Fedora 13 File Systems
• File system checking and repair:
– File corruption and OS errors:
• Caused by power losses or non-graceful shutdowns
• File system buffer cache out of sync with disk
– Buffer cache: memory used for quick data access
– fsck command:
• Checks for and repairs errors
• Syntactically similar to the mkfs command
• Example: fsck -t ext3 /dev/sda2
• Exit code returned provides description of error
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Managing Fedora 13 File Systems
(continued)
Table 5-4 Exit codes for the fsck command
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Managing Fedora 13 File Systems
(continued)
• Disk usage management
– df command:
• Used to report disk space usage of a file system
• Syntax: df [OPTION]... [FILE]...
– du command:
• Used to specify disk usage of each file
• Syntax: du [OPTION]... [FILE]...
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Managing Fedora 13 File Systems
(continued)
Figure 5-21 Output of df command
Courtesy Course Technology/Cengage Learning
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Swap Space Management
• free command used to:
– Display amount of free and used memory
– Manage swap space
• Swap space is used to implement paging
• Paging:
– Pages written to disk when physical memory is low
– Pages read back into physical memory when needed
– Helps PC performance
• Swap partition can yield better performance
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Swap Space Management (continued)
Figure 5-23 Displaying free space for memory and swap file systems
Courtesy Course Technology/Cengage Learning
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Managing Fedora 13 File Systems
(continued)
• Disk quota
– Alerts system administrator before a user consumes
too much disk space or a partition becomes full
– Fedora 13 can restrict disk space by implementing
disk quotas
• Security
– Configure by adding permissions to directories and
the objects they contain
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Summary
• Storage areas on hard drives are used to store
programs and data
• NTFS provides options for:
– Journalizing, compression, encryption, security,
auditing, and quotas
• Windows 7 uses:
– Disk Management console to manage storage areas
• Fedora 13:
– Uses partitions on a hard drive to store information
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Summary (continued)
• Windows 7:
– Handles the mounting of drives (except USB drives)
• Fedora 13:
– You can mount devices when they are needed
• Windows 7 and Fedora 13:
– Tools are available to manage file systems:
– Management tasks include:
• Reporting information about disk space availability
• Cleaning up temporary files
• Managing disk space quota
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