Google, google groups, docs for the processor used on the drive, programming
courses, some electronics, a little bit of machine design, it's not
something you're going to learn from one do-it-yourself book.
A lot of it comes under the heading of Dark Arts aka trade secrets.
Hate to burst your bubble, but anybody that would even ask this type
of question should consider some other venture. If you wanted to get
into repairing timepieces, would you post a similar request to
alt.rolex, and expect to find all the information you need to go into
business w/o years of hands-on experience.
If you insist, then I suggest you get a job with a company such as
Xyratex that makes the disk testing and servo/tracking hardware that
the manufacturers use. You can revisit this issue after you have
several years experience. Warning, if you get a job with a company
such as OnTrack which does data recovery, then they'll probably make
you sign trade secret and non-compete agreements should you resign.
If, however, you want to limit yourself to recovery where the hardware
is fine and data is corrupted or loss due to human error, then I'd
start by reading up on file systems and data layouts. Then you're
going to need heck of a lot of code written. All of it will be
custom.
I write some code to reassemble data from a certain brand of RAID
controller in event the firmware "lost" the configuration, and had to
get rather creative in looking at data patterns, physical/logical
address mapping, plus I had to utilize information that is only
available under non-disclosure. I also had to figure out filesystem
markers and configuration information once I rebuilt the raw LUNs.
The code was difficult to write, and I still have to tweak it
sometimes when I'm called upon to recover data.
So no free lunch, even if you are prepared to turn people away because
there is a hardware problem. You're going to have to write a lot of
code, and become familiar with operating system internals. At least
all of that is published.
Then, God forbid, should you get a customer willing/desparate enough
to try you out, what happens if you botch things up so somebody like
OnTrack has to charge thousands of dollars more to recover? Hope you
have insurance. (Which you won't get because the insurer won't be
stoooppid enough to write a policy for a business who has no
experience in the field to begin with).
