The reasons for damaged data on an external hard drive can be very different and range from virus attacks, unexpected system crashes and application errors as well as faulty power supply, corrupted or lost partition or system structures to accidental deletion or formatting and mechanical damage to the magnetic disk (head crash) at HDD’s. Therefore, recovering data on an external hard drive requires extreme sensitivity and also depends on the particular triggers of the data loss.
Recovery of the data
In the event of a software-based data loss, it is essential to ensure that the external hard drive is no longer being used to avoid further damage and loss.
This means in plain text that the hard disk should not be connected to the running system. Because the operating system constantly reads data regardless of the really active use of the external hard disk and will recognize deleted data as free memory and overwrite it – which thus drastically reduces the chance of a successful recovery depending on the access error.
Own recovery attempts always carry a risk! In case of doubt, professional help should be consulted to recover data on the external hard drive.
Note: If the data on the external hard disk was corrupted by a virus or other malicious software, it is essential to clean the operating system of this beforehand. In some cases it may be necessary to reboot the entire system. Otherwise, recovery of data from the infected system cannot be guaranteed.
1. External hard disk is not recognized
Basically, you should first make sure that the external hard disk is supplied with sufficient power via the USB ports. For this purpose, the respective connections on the external drive and the computer as well as the connection cables can be checked very easily. If the operating system does not recognize the external hard disk at all, a driver problem should be excluded first of all.
Under Windows, the functionality of the external data medium can be analyzed and restored in the data medium management without external software. What can be done if the hard drive is not recognized can be read in the following article: External hard drive is not recognized.
The free tool "USB-Deview" also provides the possibility to uninstall the drivers of the reserved devices of the respective USB port to eliminate possible driver conflicts between different USB devices when using the same slot.
Link to the tool: USB-Deview
The external hard drive should be removed from the USB port before uninstalling and then reconnected for independent driver installation.
If the device is still not recognized, it can also not be excluded that the firmware or possibly even whole components of the hard disk are damaged. If this is the case and important data has to be recovered, the way to a specialist is most advisable.
In case of sensitive data, a clone of the damaged external hard drive should be made before any recovery attempts are made by third-party software – if no image is available to fall back on.
In a clone, the entire contents of the hard disk are copied as a single duplicate to migrate one drive to another – in addition to files, partition tables and the Master Boot Record (MBR) are also backed up to the new volume. The following programs can be used for this purpose: DriveImage, Clonezilla and Data Rescue 4
What is needed?
In addition to the external hard disk in question, a second new hard disk drive is of course also required for cloning. Ideally, the existing data is transferred directly to a larger hard disk – but this is not absolutely necessary depending on the data volume.
Next, a software is used to clone the data – handling it always requires the utmost caution.
Highly recommended is especially the free open source clone software CloneZilla, which requires some basic PC knowledge. CloneZilla is a cross-platform live system and is not installed as software on the PC, but is downloaded as an ISO image or ZIP file and burned onto a CD, a USB stick or loaded onto a new hard drive.
Afterwards the PC must be restarted over the respective new data medium – possibly the boot over the CD or the USB device must be permitted for it in the BIOS. However, after getting the tool up and running, it is relatively easy to create a clone or even restore previously made backup files using the simply designed user interface. Further instructions for this tool can be found in a detailed walkthrough with more screenshots on the CloneZilla website. Link: CloneZilla Guide
EaseUS Todo Backup
Also EASEUS platform-independent software for sector-wise cloning of partitions of an external hard disk is suitable for beginners as well as advanced PC users due to its versatility. Like CloneZilla, the software is not installed locally, but is started via a bootable data medium. There are also very detailed instructions for the correct execution and creation of a clone: EaseUS Todo Backup Instructions
The created clone on the new hard drive can now be scanned for deleted data on the external hard drive with recovery software and then recovered. The most important steps are done by the program itself, which makes it very easy to use. If files are still missing, it may also be advisable to scan the storage medium for data with various software programs.
EaseUS Data Recovery Wizard (Free Edition)
EaseUS offers professional help for recovering deleted or damaged data as well as for creating a clone on any system beforehand.
Finally, all you need to do is launch the downloaded application executable and specify the appropriate file types to be recovered and scanned for. Finally, the data medium with the clone of the damaged external hard disk is selected and the scan process starts with the possibility to examine the recovered data in a preview after the process is finished. Link to the tool: Data Recovery Wizard
The recovery tool Recueva is particularly well suited as freeware for a quick and easy recovery. You can download it here: Recueva website.
Above all, the small program is very self-explanatory and, in addition to data on external hard drives, can also recover files from memory cards, USB devices and portable media players up to a size of 3 terabytes. In addition, Recueva is also available as a portable version, which eliminates the need for installation. All Windows versions are supported by regular updates – even including Windows Server versions. The possibility of a "deep scan" under Recueva also covers all the information technology bases for recovering files – so even the data deleted months ago can be found again. After running the program, you can select the type and location of the corrupted storage path of the data to be recovered. After Recueva has successfully completed the scan, the chance of recovery is displayed in color next to the file names. A green dot indicates an excellent chance of success in recovering data from the external hard drive, while an orange dot indicates acceptable success and a red dot indicates unlikely success – but this should not be a problem, because even if the chances of recovering data are indicated as poor, successful recovery is not that unlikely. An advanced mode and the "wizard mode" are explained in more detail on the somewhat confusing page of the provider. Link to the detailed manual: Recuva manual.
Zero Assumption Recovery
Another good alternative is Zero Assumption Recovery – also available as a demo version, where the recovery is limited to a maximum of four folders on the external hard drive. You can find the versions on the Zero Assumption Recovery website.
The restoration of images is basically free of charge and without functional restrictions. The tool is installed regularly and then offers the possibility of "Image Recovery", "Data Recovery for Windows and Linux" and "RAID Recovery". The structure and process flow of the program are not much different from the previously presented tools. ZAR also provides a preview of the files to be recovered after going through the scan and finally copies the data to a selected destination folder. Click here for the guide: Zero Assumption Recovery guide