The most common data recovery scenarios involve an operating system failure, malfunction of a storage device, logical failure of storage devices, accidental damage or deletion, etc. (typically, on a single-drive, single-partition, single-OS system), in which case the ultimate goal is simply to copy all important files from the damaged media to another new drive. This can be accomplished using a Live CD, or DVD by booting directly from a ROM or a USB drive instead of the corrupted drive in question. Many Live CDs or DVDs provide a means to mount the system drive and backup drives or removable media, and to move the files from the system drive to the backup media with a file manager or optical disc authoring software. Such cases can often be mitigated by disk partitioning and consistently storing valuable data files (or copies of them) on a different partition from the replaceable OS system files.
Another scenario involves a drive-level failure, such as a compromised file system or drive partition, or a hard disk drive failure. In any of these cases, the data is not easily read from the media devices. Depending on the situation, solutions involve repairing the logical file system, partition table, or master boot record, or updating the firmware or drive recovery techniques ranging from software-based recovery of corrupted data, to hardware- and software-based recovery of damaged service areas (also known as the hard disk drive's "firmware"), to hardware replacement on a physically damaged drive which allows for the extraction of data to a new drive. If a drive recovery is necessary, the drive itself has typically failed permanently, and the focus is rather on a one-time recovery, salvaging whatever data can be read.
The term "data recovery" is also used in the context of forensic applications or espionage, where data which have been encrypted, hidden, or deleted, rather than damaged, are recovered. Sometimes data present in the computer gets encrypted or hidden due to reasons like virus attacks which can only be recovered by some computer forensic experts.
Physical damage to a hard drive, even in cases where a head crash has occurred, does not necessarily mean there will be a permanent loss of data. The techniques employed by many professional data recovery companies can typically salvage most, if not all, of the data that had been lost when the failure occurred.
Most physical damage cannot be repaired by end users. For example, opening a hard disk drive in a normal environment can allow airborne dust to settle on the platter and become caught between the platter and the read/write head. During normal operation, read/write heads float 3 to 6 nanometers above the platter surface, and the average dust particles found in a normal environment are typically around 30,000 nanometers in diameter.[6] When these dust particles get caught between the read/write heads and the platter, they can cause new head crashes that further damage the platter and thus compromise the recovery process. Furthermore, end users generally do not have the hardware or technical expertise required to make these repairs. Consequently, data recovery companies are often employed to salvage important data with the more reputable ones using class 100 dust- and static-free cleanrooms.[7]
A common misconception is that a damaged printed circuit board (PCB) may be simply replaced during recovery procedures by an identical PCB from a healthy drive. While this may work in rare circumstances on hard disk drives manufactured before 2003, it will not work on newer drives. Electronics boards of modern drives usually contain drive-specific adaptation data (generally a map of bad sectors and tuning parameters) and other information required to properly access data on the drive. Replacement boards often need this information to effectively recover all of the data. The replacement board may need to be reprogrammed. Some manufacturers (Seagate, for example) store this information on a serial EEPROM chip, which can be removed and transferred to the replacement board.[8][9]
In some cases, data on a hard disk drive can be unreadable due to damage to the partition table or file system, or to (intermittent) media errors. In the majority of these cases, at least a portion of the original data can be recovered by repairing the damaged partition table or file system using specialized data recovery software such as Testdisk; software like ddrescue can image media despite intermittent errors, and image raw data when there is partition table or file system damage. This type of data recovery can be performed by people without expertise in drive hardware as it requires no special physical equipment or access to platters.
Sometimes data can be recovered using relatively simple methods and tools;[12] more serious cases can require expert intervention, particularly if parts of files are irrecoverable. Data carving is the recovery of parts of damaged files using knowledge of their structure.
After data has been physically overwritten on a hard disk drive, it is generally assumed that the previous data are no longer possible to recover. In 1996, Peter Gutmann, a computer scientist, presented a paper that suggested overwritten data could be recovered through the use of magnetic force microscopy.[13] In 2001, he presented another paper on a similar topic.[14] To guard against this type of data recovery, Gutmann and Colin Plumb designed a method of irreversibly scrubbing data, known as the Gutmann method and used by several disk-scrubbing software packages.
Solid-state drives (SSD) overwrite data differently from hard disk drives (HDD) which makes at least some of their data easier to recover. Most SSDs use flash memory to store data in pages and blocks, referenced by logical block addresses (LBA) which are managed by the flash translation layer (FTL). When the FTL modifies a sector it writes the new data to another location and updates the map so the new data appear at the target LBA. This leaves the pre-modification data in place, with possibly many generations, and recoverable by data recovery software.
Sometimes, data present in the physical drives (Internal/External Hard disk, Pen Drive, etc.) gets lost, deleted and formatted due to circumstances like virus attack, accidental deletion or accidental use of SHIFT+DELETE. In these cases, data recovery software is used to recover/restore the data files.
Recovery experts do not always need to have physical access to the damaged hardware. When the lost data can be recovered by software techniques, they can often perform the recovery using remote access software over the Internet, LAN or other connection to the physical location of the damaged media. The process is essentially no different from what the end user could perform by themselves.[19]
So, you just accidentally deleted or lost some files? Maybe the files were stored on your PC hard drive or external storage like a flash drive, SD card, etc. And you also learned that data recovery software might be able to help.
Before you read the list though, check out these practical data recovery tips to increase your chances of recovering the data. Saving additional data to the disk drive in question could overwrite your deleted data, making it difficult to restore your lost information.
Another powerful, yet free data recovery utility. Puran File Recovery works great to rescue data from practically any storage medium. The software supports ten different languages. All Puran utilities are totally free for private and non-commercial use. You can see a video tutorial from YouTube here.
Hi,
I found Recuva is not a free version. It works only for 500MB as free. I need your suggestion to know the best free tool to recover data in a unallocated external hard drive. My hard drive is not listed in the windows explorer. But few data recovery tools recognize that.
Some of these are good options if your budget for data recovery is limited and you only need a logical recovery. Also, keep in mind that if your data is important you may look for a data recovery specialist since any DIY attempt may cause more damage to the data.
Regarding professional data recovery services, unfortunately I have never tried such service so sorry I am unable to recommend any. I heard that many are actually scams, especially those remote ones. If you decide to try, search on Google and if possible visit several local service providers in Bay Area. Then decide to go with the one you trust.
There are many data recovery software tools to choose from, some free and some paid. When selecting a data recovery tool, make sure to double-check that it can recover PDF files, and always read online reviews to avoid poorly performing tools.
PhotoRec is an open-source data recovery software application with a command-line user interface. It supports all common file formats and file systems and can handle even fairly complex data recovery scenarios.
Disk Drill is a paid data recovery software application that you can use to recover up to 500 MB of data for free, which should be more than enough for many PDF files. Disk Drill boasts a polished graphical user interface and support for over 400 file formats, as well as all commonly used file systems.
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