Interview with Martin Hiller, Head of Kroll Ontrack Clean Room Böblingen, Germany
Q: A lot of computer users nowadays inform themselves about what to do in case of a physical hard disk drive failure via websites, blogs, forums etc., instead of immediately contacting a professional data recovery service provider. In many cases they download and try to use really specialized tools to access hard disk drives that are even physically damaged after they unsuccessfully tried out software data recovery tools. What do you think of that?
A: You´re right, there are a lot of tools to “fix” physically failed hard disk drives freely available in the internet, which are really sophisticated. But since some of them can really access the drive on a low level, they are also somewhat dangerous tools. When you do not know what you are doing, you can do a lot of harm to your drive and the data.
Q: Why is that so?
A: In a lot of cases where the hard drive isn’t working anymore, we find that the culprit is typically the hard drive head. In this case the typical user can’t do anything at all. These other cases are – and they are much more often – when the magnetism field strength on a specific location on the coated plate is not high enough anymore that data can be read out or disappeared at all. Then the automatic failure reduction of the hard disk will come into play: If the failure reduction of the specific hard disk cannot solve these reading failures, it will write error logs into their error table. The more errors the hard disk will find, the more error logs it will write into the table. If there are too many errors, then the table will be overflown and result in the hard disk drive not starting anymore.
Q: What can the user do then?
Mr. Hiller: To be honest, in this case they should at best consider getting in touch with a data recovery expert. I know that there are several free – very specialized – tools available for download on the internet to access the error table of hard drives. With these tools the user is able to access the so-called service area of a hard disk and the error or defects table. But I strongly warn doing that without the proper knowledge.
Q: Why do you warn against that method?
A: With these tools it’s possible to reset or even clear the error table. The error table consists of two different lists: the growing error table (G-List) and the P-error table (P-List). Simply put, the P-List contains the info about permanent defective sectors (bad sectors) on the drive, where data cannot be stored anymore since these sectors are prohibited to access by the operating system. The G-List saves information about sectors, which have become corrupted while the disk is in use. While it’s possible to clear the G-List without affecting any data (since they’re still on the same disk space), you can make data recovery a nightmare by changing or deleting items off the P-List. In doing so, you automatically change the addresses of the stored files on the disk. If you’re lucky, your drive will power up again and your data will be somewhere else on the disk. If you aren’t so lucky, your drive still won´t start and now your files are harder to find by an expert. In many cases where the P-List was “corrected,” it’s almost impossible to access the drive again.
Some tools offer the possibility to upload another P-List of a hard disk of the same brand to make it start again and to access the drive by the computer operating system. If this does not work, data recovery specialists can, in most cases, still retrieve the disk and the stored data. But this depends on the specific case.
Q: What is your advice then?
A: If you’re an ordinary user – either in your home or even in the IT department – and you’re not in the data recovery field as a profession, you should not try to repair the hard disk by yourself – even if you have the most specialized tools available on the market. Chances are great that your effort will not work out and data is lost forever.
On the other hand, if you don’t care too much about your data and you want to see what will happen when you change the error table settings, then try it out at your own risk with an old hard drive. If you’re successful in starting up the disk again and regaining complete files after that, then you might want to consider a job in data recovery.
But the best advice is to still use the normal S.M.A.R.T. tools provided by your hard disk to regularly check the quality and life expectancy of your drive. If there are too many bad sectors and the life expectancy is quite low, it’s time to back up your data and buy a new drive. This way you avoid having problems and losing data in the end.