So. I defrag this pc for what i think is the first time ever. I used smart defrag 2.01. Then when i restart it it tells me hard drive crash is imminent. It had never given me this error before and the pc is less than a year old. So either a defrag session caused the hard drive to fail, or it is an error. I fire up hd-tune and according to smart data, "too many" sectors had been RE-allocated. If i am not mistaken, this is what defragging does, right? reallocating sectors? i ran the error scan and no sectors were flagged bad. Is there any way i can somehow reset the smart data on a hard drive so when the hard drive actually does start to go bad it will give me a useful warning?
From what I know, you can't mess with SMART data. The data is being generated by the HD controller for the controller. The only way to reset the data would probably be to reflash the drive with a new firmware, but I would not suggest doing that just for a report.
The drive reallocates sectors when it finds that it's getting errors reading them. It moves the data from the suspect sector to a spare sector so as to protect the data from being lost if the suspect sector becomes unreadable. This is done at the hardware level inside the drive itself completely independently of the OS and file system.
Defragmenting a drive attempts to move the blocks of a file around so that they're all contiguous. This is done at the OS and file system level, and has nothing to do with whether the blocks are readable or not.
To draw an analogy - defragging is like having a stack of business cards that you dropped on the ground - you have to pick them up and sort them back into order so that you can find cards quickly when you need to. Whereas sectors that are reallocated by the drive would be similar to what happened if some of the business cards you dropped ended up in a puddle - you'd want make a copy of those cards because the ink got smudged and you're having a hard time making it out.
SMART data on the drive tells you about the sector reallocation done inside the drive - it has nothing to do with defragging. "Reallocated" sectors are those which the drive has successfully read and moved to spare sectors for safety. "Pending Sectors" are sectors that the drive is unable to read - that's data that's basically been lost because the drive can't make sense of the bits.
If the reallocated or pending sector counts in the SMART data are increasing over time, then your drive is suspect and it would be a very good idea to back up all the data you can and then replace the drive.
Although the effect of defragmenting the drive and of reallocating bad sectors are distinct and separate, what likely happened is that in defragmenting the volume the drive was asked to read a lot of sectors that were marginal, and that's what triggered the bad block reallocation. The same thing can happen if you run a full backup of the volume - the drive will have to read every sector and if it has trouble with some of them then that will trigger reallocation.
I don't know of any way to reset the SMART data. Personally it's something I wouldn't want to do, I'd rather know the real state of my drive rather than trying to make it look OK when it isn't.