A friend of mine has this external 500gb hard drive and he said that recently, when he plugged the drive, windows asked to format it so it could be readable. It looked like it was working fine before, and suddenly windows wouldn't recognize it properly. So I've got it right now and I'm trying to figure out what's happened.
First of all, I tried chkdsk /f/r which showed up lots of issues in the drive, but managed to go all the way through in some hours. But I still couldn't acess the drive, so I used HDDScan and HDD Regenerator, both showed me lots and lots of bad sectors. HDD Regenerator spent 10 hours working and 'repaired' kind of 100mb. I guess it's a pretty damaged situation. The HDD was half full by the time it got this way.
Right now, I've tried some data recovery tools which indicate there are some I/O errors trying to get the files...
Do you think it's possible to keep the data? Which programs seem apropriate?
Another thing, formatting it low level will solve these bad sections for the future?
How long has the hard drive been on? (during its entire lifetime)
If it exceeds 1500 days (4 years) on good-quality hard drives or 700 days (2 years) on really cheap ones, it would be normal, since all hard drive usually fails after some time.
In my case, my old Maxtor HD got 600 bad sectors after 1800 days, which render it pretty useless, since a sector is 4MB, 4x600 = 2.4GB.
So it means 2.4GB is bad from a 45GB Hard Drive.
In your case, it seems that the Master File Table has been corrupted, that can explain why it has a feel of "sudden" bad sectors.
When a hard drive has bad sectors, it can go undetected if you don't have a proper SMART Monitoring program, until the MFT gets corrupted and restricting you from accessing your important files. Usually when it gets to this point with a NTFS drive, your Hard Disk is really damaged, since the NTFS file system keeps 3 copies of the MFT.
A good SMART Monitoring Program is Hard Disk Sentinel, it is one of the best Hard Drive monitoring tools out there, but you have to pay.
A free alternative can be "Active@ HD Monitor" (http://www.ntfs.com/disk-monitor.htm).
Then Check the health status of the Hard Drive.
Normally, the Hard Drive will remap the bad sectors to spare sectors in the inner part of the disk. Those remapping, especially when data is unreadable, makes the reparing process very very slow, which can take over 60 hours if you got yourself lot of bad sectors.
The best you can do is use a program that fixes Bad sectors, rather than one that only remap it. HDD Regenerator is the best out there. (which I see you are already using)
This article can help you : How to remove bad sectors from a Hard Drive.
After doing that, IMMEDIATELY backup your files. Important ones first, since you don't know what is causing this problem, the Hard Disk may completely fail anytime, anywhere, and "destroying" your data.
If SMART detects only Bad Sectors, it may be a malfunction, a discalibration, a manufacturing defect, or physical abuse of the Hard Drive that may have caused a Head Crash (when the reading head touches the Hard Drive and destroys the disk surface), you can keep using the Hard Disk, but keep an eye on further signs that leads to failure. ALWAYS REMEMBER TO BACKUP YOUR DATA VERY OFTEN!
If it detects more signs that leads to Hard Drive Failure, like Spin Up time, and Spin Retry Count, the Hard Drive will fail completely very soon.
Also, as a last question, do you hear abnormal sounds coming from the Hard Drive recently? Like clicking or whining sounds?
-Good luck repairing your Hard Drive, and hope it helps!
Thanks a lot for the amazing insight, bloc97. It's been very clarifying.
I talked with the owner and he said I could format it. I guess he's more worried about the disk itself than the data. So, I tried a quick format through windows 7 and I can acess the disk. The results from the free trial of HDS are very disturbing as follows: http://imgur.com/a/ShV31
So, back to the practical issue, then. A through format or LLF would still render the drive useable for some time? I feel HDD Regenerator would take a few dozens of days to work this out, since it took 10+ hours to go through a few hundreds MBs worth in sectors...
Only powered on for 10 days, and already that much read error rate?
There is a serious problem with the disk's head, and I can guess that it did crash on the platters.
So there is no use to try to repair the disk, it is only expected to get worse. It will get to a point that the head won't work at all and transform the new Hard Drive into paperweight...
I am sure that warranty is applicable to this hard drive under those circumstances, except if the hard drive had been physically abused. (Thrown, fell on the ground, etc.)
So don't bother repairing it, tell your friend that his best bet is to get a replacement.
Fun fact, those seek times are really disturbing... It is like reading from punched tape...