I was asked to help a friend recently whose hard disk was dying. The system wouldn't boot anymore with the BIOS reporting disk or read errors. Ironically this starting happening the moment after my friend mentioned to his girlfriend that they should "really start doing backups".
Things didn't start out well. I booted using one of the rescue disks and tried mounting the failing hard drive. The
mount process hung and
dmesg showed the kernel spewing out IDE related error messages at a great number of Hz. I ended up having to forcibly kill the
mount process. Several more attempts failed in a similar way.
I had heard that failing hard disks can sometimes be made to work if cooled down. The theories about why this works seem flimsy (something about contracting the metal inside the drive so that components go back into alignment), but since options were limited at this stage I figured it was worth a try.
The new hard disk went into the computer and the faulty one was installed into the enclosure. I then wrapped the enclosure in several plastic bags and put it into the freezer with the cables hanging out of the door. With fingers crossed I connected the enclosure to the computer and turned everything on. This time I was able to mount the disk from the rescue disk without even a single kernel error. I couldn't believe it! I hurriedly partitioned the new drive and began copying before something went wrong.
There was a lot of data to copy (56GB). This gave plenty of time for worrying thoughts like "what if condensation occurs inside the cold drive and the electronics short out?". Fortunately all went well and every byte was recovered from the failing drive. After a bit more fiddling with
boot.ini, NTFS conversion and incorrect file attributes the system was working normally again. Great!
After all this, I did some research to see if other people use this trick with success (one might question why I didn't do this research before I tried it...). It turns out that in most cases it does work. I'd love to hear a solid explanation of why...