I learnt the hard way and paid £700 to recover a failed 750GB drive.
There was about 350GB of data of there.
I sent it away and was quoted £950 for the recovery as they said they needed to transplant new heads using a special machine and then clone the disk.
I agreed, paid them and they produced a report of the data that was OK and what was corrupted....about 200GB of data at around 90% integrity. I was gutted but it included a large chunk of the non replaceable data. I send an identical disk for them to close the data to and I get them back in the post a few days later.
I popped the new disk with the data on to see for myself what was there and the drive was clicking!!! In a stress I thumped it and it sprung back into life. I looked at the data and it all seemed there, not just the 200GB. I checked the email again and it was files that were missing (I had 10,000-ish images all sequentially numbered) were all showing.
I was pretty happy and I was about to create a RAID1 array with a third disk I bought when someone pointed out that I had an old disk connected as the other has the warranty seals still on it.
I contacted the recovery people and asked what had happened and they swore black is blue that the data was not retrievable, so I sent him a quick screen capture of me opening random files! In the mean time I created the RAID1 array with the 2 newer disks and copied the data over fast. Towards the end the drive started to slow and eventually it gave up after 307GB was copied off.
I got the following reply as an email from them:
"It's quite surprising that you have managed to recover even more data with your basic pc. I am quite tempted to offer you employment but on a serious note it seems that the new heads are extremely unstable, working then not working unpredictably. This can also appear to be deteriorating media. I believe the disk started to function again because it had not been accessed for an extended period of time but what you have experienced may happen once every 10000 recoveries.
The 200 Gb of data on the first file list may contain some of the images which are missing. I suggest you check the file list. The second recovery attempt integrity was estimated to be 97% because that is how many of the
1.4 billion sectors we successfully cloned. The data which is corrupt must have been stored on 3% which we were unable to clone due to the combination of malfunctioning heads/unreadable sectors.
If you have managed to save a further 107 GB, it would be useful if you check the file list 1 to see what other data you are missing. You can then return the failed drive to us for us to perform another recovery attempt for the missing data direct from the disk surface as this seems to be the best way to save the data.
Please indicate how you wish to proceed."
As it'd taken do long to get to this point I said to leave it.
I got a letter a few days later saying that they'd miscalculate the cost and a cheque for £250.
Since then I now keep the stuff I can't replace on a RAID6 array that is backed up to 2 separate USB disks once a week - one is kept in the house, and the other is kept in my garage (not attached to the house). I don't not want to go through the hassle and expense of losing data when it can be easily avoided.
If it helps, I used Datatrack Labs so I'd avoid them if you can.