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David2213 · Apr 28, 2006, 03:45 PM

Im trying to recover some data off a damaged HD and when i scan it, it says i have a bad block. what does that mean? thanks for the help

Tomchu · Apr 28, 2006, 03:48 PM

It means there are locations on the hard drive which cannot be used because they're bad -- ie. physical defects.

Nai no Kami · Apr 28, 2006, 04:29 PM

What are you trying to recover with?. If you haven't, give Data Rescue II a spin. It could recover almost all my data from an officially dead HD which wouldn't even mount.

David2213 · May 1, 2006, 06:50 PM

I've tried both Data Rescue II and Disk Warrior but neither of them worked. Will a reformat save the drive or does "bad block" mean the drive is now scrap???? Thanks

Tomchu · May 1, 2006, 07:06 PM

No utility will recover data from a bad block. A bad block is a bad block ... ie. it's physically bad.

Generally, a hard drive should have no bad blocks. If your drive does develop any, it could be on its way to the grave. I would back everything up that's on it, buy a new drive, and continue to use this drive as a spare for non-vital data to see if it gets any worse.

Tuoder · May 1, 2006, 07:27 PM

If you can't get your stuff off of it, just give it the ax. I have tried to use HDDs with bad blocks before. It is just a matter of time before a whole bunch of other blocks go bad.

David2213 · May 2, 2006, 11:12 AM

Im pretty new to all this so sorry for all the questions. This is an internal drive in an external case. Could the case cause these kind of problems? Should i just get a new internal HD and put it back in the case or just scrap the whole thing? Thanks for the help.

Spliff · May 2, 2006, 01:59 PM

All hard drives have spare blocks or sectors. If you do a low-level reformat (zero all data) of the hard drive, the spare blocks will be used and the bad blocks will be re-allocated (i.e., not used). But if the damage is too severe, the zero all data reformat will fail.

However, once a hard drive develops bad blocks, it's not advisable to keep using it for essential data as more bad blocks can develop. If the data on the hard drive is not essential, then keep using it.

Re: did the external case damage the HD? Possibly. You might want to see if there is a firmware update available from the manufacturer of your external case.

Tomchu · May 2, 2006, 02:13 PM

Bad block re-allocation is done automatically and internally by the hard drive. A user-level format will not do a thing. Low-level formats can only be done at the factory.

Spliff · 03:20 PM

Originally Posted by Tomchu

Bad block re-allocation is done automatically and internally by the hard drive. A user-level format will not do a thing. Low-level formats can only be done at the factory.

Really? That's the first I've heard of automatic re-allocation. Why does Intech SpeedTools offer to re-allocate if it's done automatically? Also, everything I've read over the years says that you have to zero-all-data in order to find and re-allocate bad sectors because that's the only way to force the system to check every sector on the hard drive.

Actually, I shouldn't be using the phrase "low level format" because it's inaccurate. I think that only SCSI drives can be low-level formatted by the user.

Update:

Okay, I found this in one of Apple own support documents.

http://docs.info.apple.com/article.html?artnum=24764

Reallocation (sparing) of bad blocks that the ATA drive tracks will occur when the block is subsequently written to. Thus the best way to force the drive to reallocate bad blocks is to initialize using the write zeros feature. Use Test Disk to verify surface integrity only. Given this strategy, there on occasion may be a need to initialize using write zeros, verify using Test Disk and if any errors occur, attempt to reinitialize using write zeros again.

Tomchu · May 2, 2006, 03:46 PM

I guess you could say that we're both correct.

The drive handles reallocation internally and automatically when it finds that it can't write to a particular block. By telling the hard drive to attempt to write to every block with a write zeroes function, you are essentially doing a search-and-reallocate of all bad blocks.

Spliff · May 2, 2006, 04:15 PM

Originally Posted by Tomchu

I guess you could say that we're both correct.

The drive handles reallocation internally and automatically when it finds that it can't write to a particular block. By telling the hard drive to attempt to write to every block with a write zeroes function, you are essentially doing a search-and-reallocate of all bad blocks.

Yup.