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The SMART data for one of my hard drives indicates that it has some reallocated sectors. I've read that a bad sector will only be reallocated on a write operation (meaning the original data is being replaced so it doesn't matter if it can't be read) or possibly a read operation (if the sector could be read subsequently after it previously couldn't be read). Based on that, a sector reallocation means that no data was lost.

But then I heard from someone that a bad sector could still result in data loss because hard drives don't verify writes. Apparently the hard drive writes the data to a sector with the CRC, and if the sector is bad then the data could get written incorrectly. The hard drive won't notice the problem until a subsequent read on that sector when the data doesn't match the CRC, and you've lost the data. Is it true that hard drives don't verify that write operations were successful?

I'm just wondering if the presence of reallocated sectors on my hard drive means I could have lost data or not.

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Can happen, if the sector reallocation did not go well then you will lose all of the data on that particular sector. But from my understanding if the relo happened properly than no there shouldn't be any loss of data. I would recommend using software such as Spinrite to check up on your hard drive.

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