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Bad Blocks

A day ago I installed an 8tb Seagate external hard drive on my iMac. Shortly thereafter I received an error message that the drive had bad blocks. I ran Drive Genius, which found that I had 172 bad blocks. Is this normal or excessive? 


I ran the Mac’s Disk Utility program “Erase” and re-formatted the hard drive then I ran “First Aid”. Both gave no error messages. Does this prevent the drive from using the bad blocks?

iMac, OS X 10.11

Posted on Dec 19, 2020 8:46 AM

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Question marked as Top-ranking reply

Posted on Dec 19, 2020 6:44 PM

If a brand new hard drive has bad blocks, then I would return it. If you are past a return window, then you will need to contact Seagate to get a warranty replacement. A brand new hard drive should not have any bad blocks. Usually when you start receiving bad blocks they will just continue accumulating. There is always a chance of data loss when a block goes bad.


If this is an older drive, then it is failing and needs to be replaced immediately.


If this drive contains important & unique data, then I hope you have it backed up. Backups are for more than the system boot drive. Any media which contains important & unique data should always have frequent & regular backups.


Edit: Disk Utility does not check for bad blocks which is why you are using Drive Genius. When you write to a bad block it will force the drive's hardware to remap the bad block so that the bad block is no longer used. In theory this would allow the drive to be continued to be used, but in reality once you get one bad block you almost always get a lot more bad blocks. Until the bad blocks are remapped the drive may spend lots of time trying to read the data from the bad block causing spinning wheels to occur in macOS.

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Question marked as Top-ranking reply

Dec 19, 2020 6:44 PM in response to Bill Wysong

If a brand new hard drive has bad blocks, then I would return it. If you are past a return window, then you will need to contact Seagate to get a warranty replacement. A brand new hard drive should not have any bad blocks. Usually when you start receiving bad blocks they will just continue accumulating. There is always a chance of data loss when a block goes bad.


If this is an older drive, then it is failing and needs to be replaced immediately.


If this drive contains important & unique data, then I hope you have it backed up. Backups are for more than the system boot drive. Any media which contains important & unique data should always have frequent & regular backups.


Edit: Disk Utility does not check for bad blocks which is why you are using Drive Genius. When you write to a bad block it will force the drive's hardware to remap the bad block so that the bad block is no longer used. In theory this would allow the drive to be continued to be used, but in reality once you get one bad block you almost always get a lot more bad blocks. Until the bad blocks are remapped the drive may spend lots of time trying to read the data from the bad block causing spinning wheels to occur in macOS.

Bad Blocks

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