Hi guys, I have a 8tb HDD with 1 out of 8 failed read head

How do you know?

you've got close to zero chance to do what you wrote without tools and extensive knowledge. 8TB drives are not the ones to start with...

pepe

You mean, you sent it to a data recovery service for a diagnosis, and now would like to try recovering the data on your own ?
If there's indeed a damaged head, short answer, no, it is not safe to do anything else on your own. However I've read that professional recovery services for helium-based HDDs (which this one probably is) was particularly expensive, so you have to decide if the data is worth the high fee. There may still be some reasonable hope to recover a good portion of the data by carefully cloning / imaging the drive with a software tool designed to deal with storage devices in bad shape, like ddrescue or HDDSuperClone. I've once imaged a 4TB drive with a bad head (it started to malfunction about halfway through the process but was probably flailing before failing for good), it looked like this. When this happens, all files which had parts or all of their sectors on the areas covered by the bad head will be incomplete or lost ; in the case of this drive, it mostly affected downloaded movies, only a few personal files, the client for whom I did this was very happy (considering that he paid me about 1/10th of what a bona fide DR company would have billed -- before sending it to me he brought the drive to a local association where they failed to get anything at all from it).

{*} Each head covers a side of a platter, 8 heads means 4 platters with 8 sides -- but files are not written on each platter until it's filled, rather, writing alternates between platters' sides every few hundred megabytes, “in serpentine fashion” (for instance 250MB on P1/S1, then 250MB on P1/S2, ..., then 250MB on P4/S2, then back to P1/S1 -- the actual pattern depends on each model, for instance Samsung drives tend to have much larger runs on each head), so a large file is bound to have damaged areas. In another case (my first paid recovery service actually), on a 1TB drive which was filled to about 1/4, and similarly had a bad head and was behaving very erratically (and it became really miserable about 1/4 of the way through, luckily by that point most of the allocated data was secured), since there were several distinct copies of most corrupted files on different locations of the drive, I was able to reconstruct the complete original file from two damaged ones, recovering about 100 more files that way (personal pictures and videos), so I got almost 100% of the user's personal files (I only got paid 50€ for the whole thing, whereas this last task alone, which is extremely tedious, would have been billed with a major extra fee by a DR company, but at least that was a hell of a learning experience !).

Only quite advanced and costly methods, used by data recovery experts, allow to do that. The cheapest solution may be the combination of HDDSuperClone with a “pro” license and DMDE, as that combo supposedly allows to selectively clone/image parts of a drive containing specific files and folders of particular interest. I've never tried that, I can't comment on how efficient it is. You could ask the author for advice, either directly or on forum.hddguru.com (he goes by the nickname “maximus”, and generally chimes in whenever one of his tools is mentioned in a thread, so if you post on the forum preferably put the tool's name in the thread's title).

Too bad you didn't get more feedback here... Perhaps try a private message.

By the way, do you know approximately how much data you had on this drive ? Was it mostly large files or small files ? Was it formatted in NTFS or another FS ?

My quick reply is that HDDSuperClone can possibly image the good heads using its self learning head skipping algorithm. But that requires a destination of equal or greater size.

It is possible with the Pro version of HDDSuperClone to use it with DMDE to extract data, and not require a destination of the full size. But it does require at least a bit over twice the size of the data to be recovered. But it is very much recommended to use a destination with the full size, unless you know what you are doing.

Also if any of the file table is in the bad head, extracting data will not work well and will require a raw recover from the best clone/image possible.

IIUC, in that other thread the DR specialist was going to disable the bad head in your helium (?) drive. Is that correct? If so, then I wonder which tool(s) they are using. AFAIK, none of the major DR tools supports these drives as yet.

I recall that @maximus experimented with certain ATA commands to detect and disable bad heads, but he found that HGST's implementation was flawed, with the result that there was an extra "phantom" head.