So far I have encountered 2 occurances of hard drive failures.

The first scenario happned to be quite a severe case of file system damage which basically rendered my data unrecovereable even after inspection from a HDD Recovery professional (http://www.ontrackdatarecovery.com.au/)

The second case was not so severe and one of the drives appeared to have a lost partition but I was able to recover all my files off it using recovery software that I downloaded.

My question is how do these HDD come about getting these logical errors. As I far as I know in these two instances there was no physical damage to the disk (disk was not clicking and no bad sectors found).

The only operation that migth of contributed to this in both of those cases of the HDD failure was copying and downlaoding large amounts of data from one drive to another. I think that these HDD's (Western Digital 2 TB 20EARS and Seagate 400 GB- not sure of the model number) would be robust enough to handle these type of operations?
The only other cause would be that these drives would of been heavily fragmented which led to the file system being corrupted as in the first scenario. What causes a drive to be heavily fragmented? I know I never run the defragment operation but does everyone that doesn't do this eventually end up with a nuked HDD drive ??

You question is pretty vast and not down to any point.

New HDDs can handle as much data as you need them to- it does not matter if you defrag 24/7 this will not nuke a hdd. if it would that means that loading windows and program everyday would nuke it in the same way.

The failures in these high capacity hdd is related to the heads or platters. The margin for error is so small that any outer variations that cannot be compensated for will cause complete disaster. (The height a head flies above the platter is like taking one of your hairs and dividing it 15 times and that's the average flight height) The platters on 1+ drives are so dense that a weak head will just cause the hdd to stop responding and go bonkers. This is 20 year technology that has been pushed to the limits by just tweaking minor technological aspects.

You want a reliable hdd go for 80GB. You want reliable high capacity storage then you need to fork out up to £1000 or more..

Otherwise just backup your stuff

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Ehm... even 80 GB drives fail

Yea... not as much as S2 Samsung 500gb's My average of those is 5 per year so far.

WD 500GB/1TB 3.5 - OMG! CRAP ALERT

I still got a 80gb seagte from 6 years ago running in off my service computers and they get chucked about

Statistics talk..;]

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What i'm trying to determine is what would of caused my file system to be damaged if it wasn't due to a physical damage of the drive? Since you are saying that it iis perfectly normal to have a drive that is heavily fragmented, the only other reason I can think of is a virus that might of corrupted the file system?

Yes- it could have been some malicious software that caused damage to your partition in one case but it might as well be caused by a unstable hard drive again.
The other was hardware failure - by the recovery centre you mentioned. Did they tell you what the problem was?
It happens daily; hard drive crashes. These things are time bombs.

In most cases if you can plug your hard drive in an enclosure and copy the data off with no hitch- then it was malicious programming causing you a pain in the backend. If that procedure did not succeed and the HDD behaved erratic-then its hardware related.

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Well that makes complete sense doesn't it? Now I see where Seagate and WD get their sales figures from

The recovery centre did not specifically say that it was caused by a hardware failure. From memory they just said that they were not able to recover much of data as my file strucure was severely corrupted. Doing a scan fo the hard drive only came up with RAW files with no meaningful filenames. But in the end they came to same conclusion like what you said - 'always back up !'

Haha.
If they managed to get to raw files that means they got access to the drive. A well equipped DR centre would have recovered what you desired most! and they were one foot in mate.

Strange. OntrackdatarecoveryAU? hmmm.

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Well techically yes, they were able to recover the files excpet that it wouldn't really been of much use to me since they had lost their filenames.

So a typical file would come as something like '0154.mp3'.

Basically they told me the recovery job wouldn't be recommended from the point after inital inspection as the only thing that could be salvaged were a heap of files with meaningless names. We are talking about thousand of nameless music tracks and video files.

Still cost me $70 AU for the initial inspection though