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My computer shut down suddenly and refuses to boot now. I started it with an Ubuntu Live CD and it reported that a hard disk failure is imminent.

The error reported by SMART:

Reallocated Sector count: The threshold value is 140 but the value is 504.

What does this mean? What should I do next?

I'm backing up all the important data to an external hard disk as I write this.

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up vote 4 down vote accepted

Basically? Yes. Good on backing everything up right away as that's the correct course of action! Get everything off the drive and decommission it.

When this happened to me, I immediately purchased new drives but not before turning off the computer that was using it as a primary boot drive. I then used a liveCD to boot up and used ddrescue to recover the disk. I didn't lose anything other than a lot of time!

I also replaced the drive with a RAID 1 array, which I recommend looking into if you can afford it, as I wasn't interested in losing that much time being down again.

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I don't think that RAID is for me as I'm running a laptop. Its still within the warranty period so I'll ask the manufacturer for a replacement. – nikhil Oct 15 '11 at 5:21
Ah yeah that won't work there :) If you want to be super careful of course, sync anything important to a desktop or cloud service so that in case of failure, you're not SOL. If extremely high security isn't a huge concern, something like Ubuntu One or Dropbox is wonderful for working with things you want to make sure you always have copies of somewhere, and can access from anywhere you have a net connection. – Anna Oct 15 '11 at 8:48

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