Data recovery on Mac under OS X

Hard drives and USB sticks can break, as can other technical parts. And sometimes it is the user's own fault if the hard drive's file system becomes corrupted. I admit that I myself have pulled an external hard drive out of the Firewire or USB connector during operation. This works fine a couple of times when the disk is not writing any data, but if you unplug it at the wrong moment, it may be in the process of rewriting the file allocation table and then has to abort because the power has been disconnected. This leads to the fact that the "table of contents" of the hard disk is defective and it no longer works properly.

Broken hard disk due to a head crash of the read / write head

The same can happen if the hard disk has a so-called head crash. This describes the fact that the read / write head of the hard disk is no longer just above the sensitive hard disk and reads data, but instead had a crash and touched the hard disk. In this case the disk continues to rotate and the read / write head damages the surface of the hard disk. Modern hard drives sometimes have a built-in mechanical protection that immediately stops and "freezes" the hard drive so that it no longer spins and the hard drive is no longer damaged. This is helpful if, for example, the hard drive falls on the floor during transport.

Regardless of how the data is lost: The result is always the same - you have mostly lost important files or the hard drive is so messed up that the system can no longer mount it. A few defective blocks on the hard drive can also be to blame if they are in the file allocation table. As a result, you usually get the message that the hard drive can no longer be read by the system and that you should format it in order to use it. Of course, you should avoid that if you want to save the data on the disk.

The first step: stay cool and make a backup of the defective hard drive

The first thing to try is to make a copy of the hard drive. This can be done with the programs "Carbon Copy Cloner"Or"SuperDuperSometimes the hard drive is so defective that it can no longer be recognized by the system. Then these two tools can no longer help either. The "TechTool Pro 6" software, which can also find files in defective blocks, offers one possibility and can also repair defective volumes. Also under the category "interesting software for restoring data" falls ""Stellar Phoenix Data Recovery 8" and "Data Rescue 3"During a test in an emergency, they have Editors from the Macworld good experience with the software "Disk Warrior"Made. It tinkered with the hard drive for two whole days, but in the end it brought a lot of files back to life that otherwise would have been gone forever.

The first step, however, should be to use OS X's own software. To do this, call up the hard disk utility and check the hard disk. You can check and repair the access rights of the volume and you can check and repair the volume yourself. If the problem is the internal hard drive from which the computer is supposed to boot, then you have to boot with a system CD, an external hard drive or a recovery partition and start the hard disk service program from there. Then the internal hard drive can also be checked and repaired.

Professional data rescuers and their costs

Of course, with these programs, too, a limit will be reached at some point and the last hope is then a professional company that offers a data recovery service. But you have to reckon with a few hundred euros in costs, which are only incurred so that the company checks whether something can still be saved on the hard drive. When the data recovery is carried out, it is not uncommon for you to come to an area where the costs for data recovery are in the 4-digit range. So I have to think in advance whether the data is so valuable that one would like to have the costs of a data recovery carried out by a professional.

Too much trial and error can make the damage worse

One thing is particularly important: Any attempt to rescue the data yourself with programs that not only read but also actively try to repair something by writing can make the damage worse. For this reason, the first step should be to make a 1: 1 copy of the hard drive or USB stick. In some cases this is unfortunately not possible because the file structure is so damaged that the backup programs can no longer cope with it. In this case it is important to decide immediately whether you would rather let a professional run it, because in that case it is best not to do anything with the hard drive in order to exclude any further damage.

But I hope that you will not get embarrassed to use such services and data recovery software, because the best recipe for data recovery is: import backup. How to make backups on a Mac with OS X easily and sensibly, I'll tell you when you read on under "Backup".


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  1. Thomas Merkle says:

    "The first thing you should try is to make a copy of the hard drive."

    Objection! If the plate makes abnormal noises, it should be disconnected (disconnected from the power) as quickly as possible and taken out of service. Then you should first research whether the noises indicate a hardware defect - if so, continued operation can dramatically worsen the condition and make (possibly professional) data recovery more difficult, expensive or impossible.

    • Sir Apfelot says:

      Hello Thomas! Objection granted. :)
      Hard disks that might have had a head crash (i.e. touching the read / write head with a disk) because the hard disk may have fallen off the table or been hit hard, should be handed over to a professional right away . If, on the other hand, a disk has been unplugged while writing and is no longer readable afterwards, you can still make a copy with some programs without any more breaking. But you should consider how important the data on the hard drive is to you. If I have important data on it that I would like to pay a few hundred to a thousand euros for in order to get it back, then I would certainly take the disk to the data saver I trust right away. This gives you the best chance that the contents can be completely restored.

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