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Data & System Management

UNIT 5

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Disk Drives

• Hard disk drive - Sealed case containing rotating disks and read/write heads

• All disks store data in basically the same way

• Disks start out as blank disks of magnetically coated metal platters

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Disk Management

• Before you can store data on a new disk, you must perform the following tasks – Create partitions on a basic disk or create

volumes on a dynamic disk– Format the disk with a file system

(FAT,FAT32,NTFS)

• A disk must be formatted before data can be written to the disk

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Partitions

• A new hard drive must first be divided in the proper size segments required by the operating system called partitions

• A partition is a physical section of a hard drive that creates a logical volume

• Each physical drive contains a partition table that shows the starting and ending address of each partition

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• A jump instruction• Name & versions of the OS files• Data structure which describes the

physical characteristics of the partition• Data structure which describes the

location of the file index• The bootstrap code

Boot Sector Information

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Formatting Disks/Drives

• Creates tracks and sectors by writing a series of F6s, (which effectively erases any data on the disk), and sector address marks to identify the beginning sector on a track

• Creates the master boot record

• Creates 2 copies of the file indexing format

• Creates the root directory

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Formatting Hard Drives• Hard drives are formatted twice• Low-level format - physically formats the

hard drive and creates tracks and sectors

• Operating system format -creates the boot record, File index and root directory on the disk

• Each partition on a drive has its own boot record, two copies of its file index and a root directory

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File Systems• The function of a file system is to map

data so it may be retrieved.• A file system must know the physical

location of data on the disk to be able to retrieve it

• Common file systems• FAT 16 partitions– up to 4 GB• Fat 32 partitions - up to 2 TB• NTFS partitions - up to 16 EB

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FAT16 File System• Features

– partitions can be no larger than 4 GB (2 GB for DOS)

– Can set permissions only on folders shared across network

– Cannot set permissions on files available locally

• FAT16 Benefits

– Compatible with most other operating systems

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FAT16 Disadvantages• Name must begin with letter or number

• Name cannot contain "/\:;|=,^*?

• Name cannot contain any spaces

• Uses 8.3 naming convention

• Does not support long file names

• Device names are reserved

• Root directory can only contain 512 entries

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FAT32 Advantages• FAT32 can support partitions up to 2 TB• It is more efficient in terms of allocating

sectors to clusters• The BIOS Parameter Block partition is larger• The boot sector stores a count of free clusters

on the partition• Does not store root directory in a set area• Uses an ordinary cluster chain• Extended partitions can hold up to 32 logical

volumes

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FAT32 Disadvantages• Not supported by all operating systems

• Only Primary partitions are bootable

• Must use FAT16 or VFAT to format shared partitions in a mixed operating system environment

• Only Windows 95 OSR2, Windows 98, ME, XP and 2000 support FAT32

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NTFS File System• Can support partition sizes up to 16 EB

• Organizes the data on disk with a relational database

• Everything on the volume is considered an object

• Every file stored on the volume is represented in a record

• Properties called streams can be added to the objects

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NTFS Advantages• Root directory can contain unlimited entries• Supports File level security• Supports File level encryption• Supports Disk quotas• Provides POSIX support• Supports individual file compression - every file

except NTLDR can be compressed• Allows auditing• Supports transaction logging• Tracks ownership• Can store files in non-contiguous memory

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NTFS Disadvantages

• Not compatible with other operating systems

• No back door access - good for security, bad for administrators

• Requires space and processing for the transaction log

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Partitions

• Partitions are assigned either a volume name or a drive letter

• Primary partitions can be made active partitions but can only be assigned a single drive letter or volume name

• Extended partitions cannot be made active but can be divided up into several logical drives with each assigned a drive letter

• There can be a maximum of four partitions on a physical hard drive (4 primary or 3 primary and 1 extended)

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• 64-byte data structure

• Located in first sector of the hard disk

• Contains info about disk partitions

• Can define up to 4 partitions per disk

• Partition Table Entries contain info on

–Whether the partition is a system partition

–Where the disks begins and ends

–Total number of sectors used

–The partition’s file system

Partition Table

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Primary Partitions

• Only a primary partition can be marked as the active partition

• The active partition is where the hardware looks for the boot files to start the operating system

• Multiple primary partitions allow you to isolate different operating systems or types of data

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Extended Partitions

• There can be only one extended partition on a hard disk

• Unlike primary partitions, you don't format extended partitions or assign drive letters to them

• You divide extended partitions into segments. Each segment is a logical drive where you assign a drive letter to each logical drive and format it with a file system

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Primary and Extended PartitionsPrimary Partitions

F:F:

E:E:

D:D:

C:C:

G:

E:E:

D:D:

C:C:

PhysicalDrive

ExtendedPartitionwith LogicalDrives

PrimaryPartitions

OR

F:

H:

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Disk Properties

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Fragmentation• After a hard drive has been in use for

awhile, files tend to be written in a non-contiguous format which means that the clusters a file is written to are not in sequential order

• Slows down file access• Hard to recover file if becomes corrupt• DEFRAG is a utility corrects the

problem and optimizes the disk

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Fragmentation Tool

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Clusters• Lost Clusters are clusters that no file

points to and occur as a result of the mapping in FAT becoming corrupted

• Cross-Linked Clusters are cluster that more than one file points to that occur as a result of the mapping in FAT becoming corrupted

• SCANDISK and similar programs will repair both of these problems

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NTFS Disk Compression• Using software to increase the amount of disk

space– Usually doubles the space

• Stores entire contents of drive as a single file• Uses a mathematical algorithm to store files

in a more compact format• Files decompress “on-the-fly”• Slows down system performance

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NTFS Encryption

• Folders are encrypted transparently• Unencrypted on the fly• If you lose the user login or forget the

password, you cannot open your files• Use encryption only for important

information

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Disk Caching

• A disk cache is a temporary storage area in RAM for data being read from or written to a hard drive

• Hardware cache is contained in RAM chips built right on the disk controller card

• Software cache is stored on the hard drive and loaded into memory as a terminate-and-stay-resident (TSR) program

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Disk Cloning

• Used to make a bit by bit copy of the entire hard disk or a single partition

• Independent of the operating or file system

• Software like Norton’s ghost or Drive Image

• Makes deploying identical workstations much easier

• Can also be used to backup computers

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System Backups• All users can backup a file or directory if

they have read permission• What Should be Backed Up? Always

– Critical files and folders– System configuration files

• Periodically– Files that rarely change

• Never– Temporary files

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Backup Media

• DAT – Digital Audio Tapes

• CDs and DVDs• DLT tapes

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Types of Backups• Full - backs up all selected files and

resets the archive bit• Copy - backs up all selected files but

does not reset the archive bit• Incremental - backs up all the selected

files that have changed and resets the archive bit

• Differential - backs up all the selected files that have changed but does not reset the archive bit

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Backup Schedule & Tape Rotation

• Typical Backup Schedule– Daily Incremental– Weekly Full– Month-End Full

• Typical tape rotation– Store daily tapes for 3 weeks on site than

reuse– Store weekly tapes for 6 months on site

than reuse– Store monthly tapes off-site for 2 years

than return and reuse

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Backup Terminology• Backup Sets - group of files and folders

from a single volume from a single backup operation

• Catalogs - lists of backup sets or members– Tape catalog - contains list of all backup

sets on a tape– Backup Set Catalog - contains list of files

and folders in the backup set• Backup Log - record of the entire

backup operation

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Driver Signing

• Signed drivers have been tested by Microsoft to make sure they work properly

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Windows Update

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Virtual Memory

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System Restore

• Built in capability of windows that creates a restore point every time you install a new device or application

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Restore CDs

• Restore CDs – put the system back to the day you bought it. All data and programs added since then will be lost but can be restored from backups

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Disk Images

• Programs like image for windows and ghost do bit copies of the hard drive or partition and make restoring easy

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Recommended Maintenance

• Do regular backups• Use antivirus and anti-spyware

software• Periodically defrag the hard disks• Don’t smoke near your computer• Use a dehumidifier in damp areas• Use caution when moving the

computer if it is running

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Data Transfer Standards

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Digital Audio

• Typical sampling rate is 44.1 or 192.4 KHz which means that it is being sampled at 44,100 or 192,400 samples per second

• Encoded using a codec into 16 bits of data

• MP3 encoding can compress the data to approximately a 10:1 ratio but there will be a loss of quality