Uses Disk image

1 uses

1.1 enhancement
1.2 software distribution
1.3 security
1.4 virtualization
1.5 system backup
1.6 rapid deployment of clone systems
1.7 legacy hardware emulation
1.8 copy protection circumvention

uses

disk images used heavily duplication of optical media including dvds, blu-ray disks, etc. used make perfect clones of hard disks.

a virtual disk may emulate type of physical drive, such hard disk drive, tape drive, key drive, floppy drive, cd/dvd/bd/hd dvd or network share among others; , of course, since not physical, requires virtual reader device matched (see below). emulated drive typically created either in ram fast read/write access (known ram disk), or on hard drive. typical uses of virtual drives include mounting of disk images of cds , dvds, , mounting of virtual hard disks purpose of on fly disk encryption ( otfe ).

some operating systems such linux , macos have virtual drive functionality built-in (such loop device), while others such older versions of microsoft windows require additional software. starting windows 8, windows includes native virtual drive functionality.

virtual drives typically read-only, being used mount existing disk images not modifiable drive. software provides virtual cd/dvd drives can produce new disk images; type of virtual drive goes variety of names, including virtual burner .

enhancement

using disk images in virtual drive allows users shift data between technologies, example cd optical drive hard disk drive. may provide advantages such speed , noise (hard disk drives typically 4 or 5 times faster optical drives, quieter, suffer less wear , tear, , in case of solid-state drives, immune physical trauma). in addition may reduce power consumption, since may allow 1 device (a hard disk) used instead of 2 (hard disk plus optical drive).

virtual drives may used part of emulation of entire machine (a virtual machine).

software distribution

since spread of broadband, cd , dvd images have become common medium linux distributions. applications macos delivered online apple disk image containing file system includes application, documentation application, , on. online data , bootable recovery cd images provided customers of commercial software companies.

disk images may used distribute software across company network, or portability (many cd/dvd images can stored on hard disk drive). there several types of software allow software distributed large numbers of networked machines little or no disruption user. can scheduled update @ night machines not disturbed during business hours. these technologies reduce end-user impact , reduce time , man-power needed ensure secure corporate environment. efficiency increased because there less opportunity human error. disk images may needed transfer software machines without compatible physical disk drive.

for computers running macos, disk images common file type used software downloads, typically downloaded web browser. images typically compressed apple disk image (.dmg suffix) files. opened directly mounting them without using real disk. advantage compared other technologies, such zip , rar archives, not need redundant drive space unarchived data.

software packages windows distributed disk images including iso images. while windows versions prior windows 7 not natively support mounting disk images files system, several software options available this; see comparison of disc image software.

security

virtual hard disks used in on fly disk encryption ( otfe ) software such freeotfe , truecrypt, encrypted image of disk stored on computer. when disk s password entered, disk image mounted , , made available new volume on computer. files written virtual drive written encrypted image, , never stored in cleartext.

the process of making computer disk available use called mounting , process of removing called dismounting or unmounting ; same terms used making encrypted disk available or unavailable.

virtualization

a hard disk image interpreted virtual machine monitor system hard disk drive. administrators , software developers administer them through offline operations using built-in or third-party tools. in terms of naming, hard disk image virtual machine monitor has specific file type extension, e.g., .vmdk vmware vmdk, .vhd xen , microsoft hyper-v, .vdi oracle vm virtualbox, etc..

hard drive imaging used in several major application areas:

forensic imaging or acquisition process entire drive contents imaged file , checksum values calculated verify integrity (in court cases) of image file (often referred hash value ). forensic images acquired use of software tools. (some hardware cloning tools have added forensic functionality.)
drive cloning, mentioned, typically used replicate contents of hard drive use in system. can typically done software-only programs typically requires cloning of file structure , files themselves.
data recovery imaging (like forensic imaging) process of imaging every single sector on source drive medium required files can retrieved. in data recovery situations, 1 cannot rely on integrity of file structure , therefore complete sector copy mandatory (also similar forensic imaging). similarities forensic imaging end there though. forensic images typically acquired using software tools such encase , ftk. however, forensic imaging software tools have limited ability deal drives have hard errors (which case in data recovery , why drive submitted recovery in first place).


data recovery imaging must have ability pre-configure drives disabling attributes (such smart , g-list re-mapping) , ability work unstable drives (drive instability/read instability can caused minute mechanical wear , other issues). data recovery imaging must have ability read data bad sectors. read instability major factor when working drives in operating systems such windows. typical operating system limited in ability deal drives take long time read. these reasons, software relies on bios , operating system communicate hard drive unsuccessful in data recovery imaging; separate hardware control of source hard drive required achieve full spectrum of data recovery imaging. because operating system (through bios) has set of protocols or rules communication drive cannot violated (such when hard drive detects bad sector). hard drive s protocols may not allow bad data propagated through operating system; firmware on drive may compensate rereading sectors until checksums, crcs, or eccs pass, or use ecc data recreate damaged data.
data recovery images may or may not make use of type of image file. typically, data recovery image performed drive drive , therefore no image file required.

there 2 schemes predominant across virtual machine monitor implementations:

the virtual disk implemented either split on collection of flat files, typically each 1 2gb in size, collectively called split flat file, or single, large monolithic flat file. pre-allocated storage scheme referred thick provisioning scheme.

the virtual disk can again implemented using split or monolithic files, except storage allocated on demand. several virtual machine monitor implementations initialize storage zeros before providing virtual machine in operation. dynamic growth storage scheme referred thin provisioning scheme.

there 2 modes in raw disk can mapped use virtual machine:

virtual mode
the mapped disk presented if logical volume, or virtual disk file, guest operating system , real hardware characteristics hidden. in mode, file locking provides data protection through isolation concurrent updates; copy on write operation enables snapshots. virtual mode offers portability across storage hardware because presents consistent behavior virtual disk file.
physical mode
in mode, called pass through mode, virtual machine monitor bypasses i/o virtualization layer , passes i/o commands directly device. physical characteristics of underlying hardware exposed guest operating system. there no file locking provide data protection.

system backup

some backup programs user files; boot information , files locked operating system, such in use @ time of backup, may not saved on operating systems. disk image contains files, faithfully replicating data. reason, used backing cds , dvds.

files don t belong installed programs can backed file-based backup software, , preferred because file-based backup saves more time or space because never copy unused space (as bit-identical image does), capable of incremental backups, , have more flexibility. files of installed programs, file-based backup solutions may fail reproduce necessary characteristics, particularly windows systems. example, in windows registry keys use short filenames, not reproduced file-based backup, commercial software uses copy protection cause problems if file moved different disk sector, , file-based backups not reproduce metadata such security attributes. creating bit-identical disk image 1 way ensure system backup original. bit-identical images can made in linux dd, available on live cds.

most commercial imaging software user-friendly , automatic may not create bit-identical images. these programs have of same advantages, except may allow restoring partitions of different size or file-allocation size, , may not put files on same exact sector. additionally, if not support windows vista, may move or realign partitions , make vista unbootable (see windows vista startup process).

rapid deployment of clone systems

large enterprises need buy or replace new computer systems in large numbers. installing operating system , programs each of them 1 one requires lot of time , effort , has significant possibility of human error. therefore, system administrators use disk imaging clone prepared software environment of reference system. method saves time , effort , allows administrators focus on unique distinctions each system must bear.

there several types of disk imaging software available use single instancing technology reduce time, bandwidth, , storage required capture , archive disk images. makes possible rebuild , transfer information-rich disk images @ lightning speeds, significant improvement on days when programmers spent hours configuring each machine within organization.

legacy hardware emulation

emulators use disk images simulate floppy drive of computer being emulated. simpler program accessing real floppy drive (particularly if disks in format not supported host operating system), , allows large library of software managed.

copy protection circumvention

a mini image optical disc image file in format fakes disk s content bypass cd/dvd copy protection.

because full size of original disk, mini images stored instead. mini images small, on order of kilobytes, , contain information necessary bypass cd-checks. therefore; mini image form of no-cd crack, unlicensed games, , legally backed games. mini images not contain real data image file, code needed satisfy cd-check. cannot provide cd or dvd backed data computer program such on-disk image or video files.