Detecting bad sectors using Delphi or freepascal

2
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Thanks to help by David Heffernan I have a program written in Freepascal (but a Delphi solution to my question would suffice) that reads a physical disk sector by sector. It does so using the Windows API CreateFileW function for the disk handle, then FileFile, FileSeek etc to navigate and read. If all the sectors are OK, it works fine. However, if the disk had bad sectors, I need to treat them differently.

My question is, is there and procedures or libraries that can be used, while reading these sectors, to determine if they are bad sectors? If not, how might I go about it? I gather it is the disk controller that knows what sectors are bad and which are not, so I don't think my program can actually access a bad sector, so how can I detect which are the bad ones and act accordingly? Does one need to query SMART and if so, how?

I have searched this site (only found this C post, which relates to a program, not code) and Googled it and no obvious solutions came to my attention.

2
delphifile-iofreepascalsector
If you haven't already, take a look at Roadkil's Unstoppable Copier. This can do a remarkable job of reading data out of bad sectors, apparently by reading the sectors over and over again, maybe dozens or even hundreds of times. Not saying that's an answer to your q, but maybe googling around it will turn up some useful info about the techniques it uses. – MartynA
It's very easy to have a bad disk sector that even the OS thinks is fine. – Graymatter
Forgive the lack of detail. I don't need to read or try to read the data in the bad sectors. Any bad sectors identified I need to treat as zero. – Gizmo_the_Great

2 Answers

3
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Generally speaking, you can't access bad sectors at all (they have been remapped already so are out of LBA). What you can access are pending sectors, attempts to read them will always cause a read error. SMART will tell you nothing but the number of bad/pending sectors. So you probably should continue using chosen API interpreting persistent read errors as diagnostics for "bad" sectors, just make sure they aren't caused by access sharing violation. If you want to obtain a p-list or g-list somehow, it is only possible (for PATA/SATA, not SCSI) in terminal mode, what requires connection to HDD's service port, USB-to-COM adapter and is vendor- and product-specific, if possible at all.

2
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Sectors and their hardware status are not things that normal user-level code needs to deal with so there is no easy copy/paste API available for this purpose.

Also in general the sector concept is abstracted away on multiple levels. For one example see the Wikipedia: logical disk address translation. Physical sector status is very low-level concept. Some hardware vendors even don't expose it through public API at all. Bad (or suspicious) sectors are often detected in the hardware itself and automatically redirected to other places. So in general the bad disk-sector concept does not exist

MSDN Logging Guidelines

...Bad sectors. If a disk driver encounters a bad sector, it may be able to read from or write to the sector after retrying the operation, but the sector will go bad eventually. If the disk driver can proceed, it should log a Warning event; otherwise, it should log an Error event. If a file system driver finds a large number of bad sectors and fixes them, logging Warning events might help an administrator determine that the disk may be about to fail...

If you really need to work with this low-level concepts then first forget about Pascal or Delphi as your requirements.

Learn how to use the Windows API and once you know it bind to the API in your language of choice (you can map any Win32 user-level API function to Free Pascal easily).

In my opinion you are going to swim in a dark & deep waters without flashlight and swim ring and you should think twice about what you (or your users) really need/want and perhaps improve the question to get a reasonably-sized on-topic answer