The most important tool you MUST have if data is irreplaceable
It is always easier to work with an image (clone) of a failed hard disk drive, than trying to read one that is failing or behaving eratically, Your operating system will be slow, attempt to run checkdisk and force the reading of areas of the drive you really want to stay away from.
The best case scenario is to create an image using a method designed to deal with failing and or unreadible sectors before using your operating system to view the data
Remember if data is important please consider the experts!
Cloning a hard drive
This is a process of sector by sector copy (cloning) of a possible failing hard drive.
When a hard drive is being read within a windows environment and encounters a bad sector, the system will automatically attempt a 32 times read of that sector before proceeding to the next bad sector and so on. This is what can cause a computer to be slow, hang or prevent from even booting.
It is imperative to have a well developed cloning system that enables not only these sectors to be read, but skipped by sector or skipped by head, sector location recorded, read time allocation ajustment control and even reverse reading, once this process is complete you can then have a diagnostic report on what exactly was wrong with the drive.
This simple utility will make a bit by bit mirror image of any drive including SCSI with any operating system to a new hard disk drive, skipping all bad sectors and simply moving to the next, enabling you to retrieve your data from a functioning hard drive instead of the volatile drive.
This tool creates a self bootable floppy disk and by simply attaching the old drive to one IDE cable and the New drive to the other IDE cable, you will soon be imaging your drive.
The Importance of Imaging
Case Scenario 1
The drive has slight platter damage or the start of a fine ring that will soon be a fatal unrecoverable ring or score across the platter.
With imaging the drive you can adjust the amount of time a read/write head will read a sector. The default for windows is to attempt to read a sector 32 times before marking it as bad and moving to the next sector. If that sector is physical damage on the platter, force read 32 times will kill the read/write heads and cause further damage. If you can adjust the read time you can quickly move across the platter making sure you read all good sectors before concentrating on the bad sectors that can cause head damage.
Case Scenario 2
You can only read 3 out of 4 read\write heads, now you can recover 75% of a drive before breaking seals and attempting internal component replacements.
If it is scored platters in non-critical areas, imaging is the first step. From experience most laptop drives can form head killing abrasive areas on a platter (see common faults). With the image process you can clone a drive from the front to this area and STOP immediately before the read\write heads go bad, then reverse clone to that point making sure to read that area of the drive last. That way you have most of the drive before risking the very sensitive read\write heads.