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How to safely diagnose physical HDD failures: interview with a cleanroom engineer

Martin Hiller

A lot of computer users inform themselves nowadays about what to do in case of a physical hard disk drive failure, usually from websites, videos, forums, etc., instead of immediately contacting a professional data recovery service provider. In many cases users try to download and use specialist tools to access HDDs that are physically damaged, after they unsuccessfully tried out other software data recovery tools.

However, what risks are involved with going DIY? How hard could it be? We caught up with Martin Hiller – Head of Kroll Ontrack’s cleanroom facility in Germany to find out exactly what you should be wary of, plus how to diagnose physical HDD failure without making things worse.

There’s so many free software tools out there – what’s your take on them?

Martin: You’re right, there are a lot of sophisticated tools to ‘fix’ physically failed HDDs, many of which are freely available on the internet. However, since some of them can 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.

Why is that exactly?

Martin: In some cases, a HDD stops working because of a head crash, which is where the read/write heads ‘crash’ down onto the magnetic platter surface, causing a severe drive failure. This can often occur when dropping a drive from a height while it’s running, but regardless; in these scenarios a typical user cannot do anything at all on a DIY basis. In the majority of cases though, HDDs can fail when the magnetism field strength on a specific location of the coated platter is not high enough anymore so that data can be read, or it could have disappeared completely. This is where the automatic failure reduction of the HDD will come into play. If the failure reduction cannot solve these reading failures, it will write error logs into its error table. The more errors the HDD finds the more error logs it will write. If there are too many errors, then the table will be overflown and result in the hard disk drive not starting anymore.

What should someone do then, if this happens?

Martin: In these cases you should consider getting in touch with a data recovery expert. I know that there are several free (and very specialist) tools available for download on the internet which allows access to the error tables of hard drives. With these tools the user is able to access the ‘service area’ of a HDD and the error or defects table. But I strongly recommend against doing this without the proper knowledge.

What’s the problem with that?

Martin: Well, with these tools it is 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 access by the operating system. The G-List saves information about sectors, which have become corrupted while the disk is in use. While it is possible to clear the G-List without affecting any data, since there are still on the same disk space, you can make data recovery a nightmare by changing or deleting item of the P-List. By doing so, you automatically change the addresses of the stored files on the disk. If you are lucky, your drive will power up again and your data will be somewhere else on the disk, if you are not so lucky, your drive still won’t start and your files are harder to find by an expert. In many cases, when the P-List has been modified it is 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 and doesn’t work every time.

So what’s your advice?

Martin: If you are an ordinary user – either at home or even in an IT department – and you do not want to get into the data recovery field as a profession, you should not try to repair the hard disk by yourself, even if you have the most specialist tools available on the market. The chances are very high that your efforts will not work out and your data may be lost forever.

If you do not care much about your data and your disk and you want to find out what will happen if your change settings in error tables, then you can try it out at your own risk with an old HDD. If you are successful in starting up the disk again and regaining complete files after that, then you might consider a job in data recovery!

But the best advice by far is still to use the normal SMART tools provided by your hard disk and frequently check the quality of your drive and its life expectancy. If there are too many bad sectors and the life expectancy is quite low it is definitely time to take preventative measures; backup your data and buy a new drive as soon as you can. This way you avoid having problems with data loss and ultimately, having to consult a specialist to help you get it back.

Do you use specialist tools to check the condition of your hard drive? Have you ever lost data by trying out free software tools from the internet? Let us know by commenting below, or tweet @DrDataRecovery

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