Telenotes 8Data Recovery and Disk Management

Chapter 4 Notes:

Hard Disk Structure;a) Physical Disk – the term used to identify hard drive installed in a computerb) Disks are formatted into tracks and sectorsc) Tracks are subdivided into sectorsd) Each track and sector is identified by a number

i) An allocation unit - A grouping of one or more sectors(1) The smallest unit of space that can be written to.(2) Fixed in size

Inside a Hard Disk

Two Types of Disks:Basic and Dynamic Disks

Basic DisksA) Basic disks used for older OS Windows 95 / 98B) Can be subdivided into partitions (Primary, Extended and Logical)

Partitionsi) Primary Partition – is used to boot the computer (up to 4 )

(a) Can have up to four primary partitions on a hard disk(b) Active Partition – the primary partition set to boot a system; only one

primary partition can be active at one timeii) Extended Partition – (up to 1) can contain files but cannot be used to boot a

systemiii) Logical Drive – Subdivision of Extended Partition

Master Boot Recordi) A Master boot record (MBR) and a Partition Table are created when formattingii) The Master boot Record contains information about the structure of the hard drive on the partition table.iii) MBR located in first sector of primary partition.

Primary Partition Types:i) System Partition (1st Primary) – where Windows 2000 boot files are stored

- Active partition ( only on 1 Primary) – will be the boot partition- Can be assigned individual Drive Letter (ex. C: )

ii) Boot Partition (2nd Primary) – where Windows 2000 system files are storediii) These 2 can be on the same partition (1st Primary)

Extended Partitionsi) Created on free space not used by primary partitionsii) Can be subdivided into logical drives

(1) Logical Drives(a) Can be assigned individual Drive Letters (ex. D: E: ) or Mounted

Basic Disc

Dynamic DisksDynamic disks have volumes rather than partitions

Dynamic Disksa) Volumes can span multiple hard drives; partitions cannotb) Volumes can be resized without losing data; partitions cannot (without special

software)c) Basic disks can be converted to dynamic disksd) Can create fault-tolerant volumes (ex. Mirrored and RAID5 volumes)

Dynamic Disk Considerationsa) Only an advantage with multiple hard drivesb) Can only be used with Windows 2000c) Laptop and removable drives cannot be converted to dynamic disks

Dynamic Disk Volumesa) 2 Types: Simple Volumes / Spanned Volumes

i) Simple Volumes reside on a single hard drivesii) Spanned Volumes can reside on multiple hard drivesiii) Disadvantage: No Fault Tolerance: If one disc crashes the whole volume is

lost.Dynamic Disk

Disk ManagementThe process of Partitioning and allocating of disk resourcesDisk Management Tool

i) Used to manage disks and partitions

Mounting Drivesi) New to Windows 2000ii) Allows for more than 26 (the number of letters) mounted drives ex.

Finance folderVolume Mount Point

(1) Maps a disk partition to a folder rather than a logical letter drive

Formatting Disksa) Formatting is setting up partition or volume so that it can accept datab) Different kinds of formatting (FAT, FAT32, NTFS)c) NTFS is native to Windows 2000

NTFSi) Supports hard disk larger than FAT/FAT32ii) Built in security using EFS (Encrypting File System) iii) File compression using H.A.S.iv) Can assign specific disk quota to a userv) Contains a Change Journal feature - allows files to be more efficiently

recoveredvi) Cannot be recognized by Windows 95/98 computers

Formatting a Drivei) Can use GUI or command line toolii) Must select file system (FAT, FAT32, or NTFS)iii) Must select allocation unit size

Converting a Formatted Drive(1) Convert from FAT or FAT32 to NTFS without losing data(2) Cannot convert back(3) Must Use the CONVERT command line tool

File Compressiona) Can be set on Files or Folders from the Properties menub) Is completely transparent to the userc) If a folder is compressed, only new files copied into the folder will be

compressed, existing files will remain uncompressed.

RAID (Redundant Array of Independent Disks)a) Has Fault Toleranceb) Standard disk storage format (method) for using multiple hard drivesc) Different types of RAIDd) Microsoft supports RAID levels 0, 1, and 5

RAID 0 (stripping)a) Also called, a Stripe Set without Parity

Parity - Process of using data bits to verify other data bits when they are written to a hard disk

Stripe Set- (same as a Dynamic Disk Volume) – Can span multiple disks, but the size of the disk sections must be equal.

b) Benefits: Increases disk performance / write / read speed.(1) Unlike Volumes, the entire Stripe on a disk does not have to be full before

writing to a second disk.(2) All information is divided into logical blocks and saved on different hard

disk drives simultaneously. Data save / loads is much faster.c) Problems: No complete fault tolerance

(1) If one hard disk drive becomes damaged then you loose information on all the hard disk drives connected to this RAID.

RAID 1 (mirroring)a) Has Fault Tolerance using: Disk mirroring

i) Same data is written to multiple hard drives(1) Benefits:

(a) Fault tolerance – If one disc fails, other disc contains information.(b) Speeds read requests – 2 reads heads compete in looking for the same

data(2)

(a) Expensive- must purchase twice as many drives(b) If both discs are connected to the same Controller, If controller fails all

data id temporarily unavailable.

RAID-0+1 (Stripping plus Mirroring)a) A combination of RAID 0 and RAID 1

i) Mirroring a Striped RAID 0 – A Basic RAID 0 is mirrored

RAID 5 (Striping with Parity) (most popular)a) Uses Parity Bits

i) Parity – data bits that keeps track of what is writtenb) Writes same data to multiple drives but leaves one drive for parity data

i) Benefits(1) If drive fails, can continue working with data from other drives(2) If drive fails, data will automatically be rebuilt onto replaced new drive

(due to parity data tacking)ii) Problems

(1) Requires a minimum of three hard drives(2) CPU and Bandwidth performance are slower

http://www.avid.com/exchange/forums/storage/14/103411/RAID%20box.jpg

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Disk Maintenance: CHKDKS:

1. Using CHKDKS (check disk) to examine sectors on the hard drive2. Will test and fix bad sectors3. Can be run on hard and floppy drives

Disk Defragmenter1. Collects pieces of files together on contiguous (consecutive) sectors 2. Improves disk performance3. Can be run on a regular basis

Disk Quotas1. Allow administrator to control amount of space used by user2. Must be configured for each volume on the hard drive3. Requires the NTFS file system to be installed4. Can set warning for users that are close to their quota5. Prevents users from saving files when their quota has been reached6. Administrator accounts not subject to disk quotas

Remote and Removable Storage1. Remote storage is used for backup devices like tape drives2. Removable storage is used for devices like ZIP drives3. Files can be moved to remote storage but have links preserved on the system4. When users access a link the remote storage device is activated and the data

restored

Purchasing a HD:

How to Select a Hard Drive Based on Specifications

Two numbers that are needed to know: size and speed. Size: in GB or gigabytes. Speed: in RPMMost consumer desktop systems come with either a 5400 rpm or 7200 rpm hard drive.

Systems which use the 5400 rpm drives tend to be slower but are used in more compact systems or systems which are designed to be silent running. It is more common to see drives running at the 7200 rpm speed as they give better performance

Interfaces: IDE and Serial ATA

The performance between the two is essentially identical at this point. The major difference really is the ease of installing the drives. Serial ATA drives have less cabling and configuration required to install a drive.

Choice should be task dependent:

Word Processing: 40+ GB, 5400 rpm Web Surfing: 40+ GB, 5400 rpm Light Gaming: 80+ GB. 7200 rpm Digital Music: 80+ GB, 7200 rpm Heavy Gaming: 100+ GB, 7200 rpm Graphics Editing: 100+ GB, 7200 rpm Digital Video: 150+ GB, 7200 rpm

Detail OF Purchasing Specs:

What to Look for in a Hard DrivePart I: Performance

Performance

A slow hard drive directly impacts all of your computing tasks. Hard drive performance is really determined by four core attributes of a drive:

1. Interface IDE / SCSI2. Rotational Speed 3. Access Times 4. Buffer Size

Two primary interfaces : SCSI and IDE.

SCSI - for high performance drive arrays and server systems and generally not found in the home computer market. Its

-advantage is its ability to handle many drives concurrently. -current SCSI standard is Ultra 160 that allows for 160 megabytes of data per second.

IDE - most common form of interface found on personal computers. - number of speeds available (from ATA/33 to ATA/133). Most

ATA/100 - The number in the version indicates the maximum bandwidth in

megabytes per second the interface can handle. ex, an ATA/100 interface can support 100 MB/sec.

- Systems are restricted to the PCI Bus speed that can only handle about 133 megabytes per second.

Problem:Handling multiple devices.

Each IDE controller has 2 channels that in turn can support 2 devices. The controller runs at the speed of the slowest device.

Ex. If Hard drive and Optical drives on same IDE, Controller runs at optical drive speed which slows performance for the hard drive.

Rotational Speed –- largest factor in the performance of the drive. - The higher the rotational speed of the drive, the more data the drive

can read and write from the - Heat and noise are created at higher rotational speed.

-Heat impacts the performance-Noise causes distractions Most rotate at either 5400 or 7200 rpm.

Access Times--length of time it takes the drive to position the drive head on the

-4 access times (milliseconds): Read Seek Write Seek

Track-to-Track Full Stroke

Read seek is generally an average time it takes to move the head from one position on the drive to another to read data from the drive. Write seek is the average amount of time that it takes the drive to move to an empty space on the disk and begin writing the data. Track-to-track is the average amount of time the drive takes to move the drive head to a new side track on the drive. Full stroke is the amount of time it takes the drive head to move from the outer to inner portion of the

-For all of these, a lower number means higher performance.

Buffer Size-- Amount of RAM on the drive to store frequently accessed data from

the drive. - Since RAM is faster at transferring data than the drive head operation,

it increases the speed of the drive. - Most drives today come with a 2MB drive buffer.

Part II: Capacity and Aesthetics

Capacity--Size of data in Gigabytes a drive can store- Every drive is made of one or more disk platters each with its own drive heads to read and write the information from the platters. (Rated capacities ex. each platter may be rated 20 GB. ) - Additional platters on the same HardDrive can increase performance as the number of drive heads to read the data is increased

Problem:-more drive heads/platters, translates into a higher ambient noise -more drive heads/platters, more energy that must be used to turn the platters at the proper speeds. Increases the amount of heat produced and can actually decrease performance

In comparison- to a similar capacity drive with fewer platters may mean a better performing hard drive.

Aesthetics -Also Called environmental specifications -All drives produce: noise and heat.

-Noise can be a distraction for people. - Slower rotational drives tend to produce less noise than higher rotational speed drives. Noise ratings are listed in decibels (dBA). The higher the number of decibels, the louder the drive is.

-Heat affects the lifespan of your computer system and hard drive. Ex. IBM Deskstar drives are only rated for temporary use. -Hard drives are usually not rated on heat