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Thread: Read the header of a disk sector

  1. #1
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    Mar 2013
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    Question Read the header of a disk sector

    Hello,

    I'm looking for a low-level linux program that I can use to read the header of a disk sector. I have an idea that dd might do it, but I'm not sure and I've been googling for a while. I'd like to be able to read the various pieces of information in that header: address identification, header parity bytes, etc.

    Also, will my ability to do this be affected by the type of file system I use? e.g., a journaling file system or otherwise?

    Thanks!

    Mag

  2. #2
    Join Date
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    Re: Read the header of a disk sector

    Hi

    Quote Originally Posted by magmaman42 View Post
    Hello
    Welcome to the forums

    I'm looking for a low-level linux program that I can use to read the header of a disk sector. I have an idea that dd might do it, but I'm not sure and I've been googling for a while. I'd like to be able to read the various pieces of information in that header: address identification, header parity bytes, etc.
    If i understand you correctly.....

    I think most of this is handled by the drives firmware and, therefore, is proprietary.

    I'm not sure if dd will do the job here.

    I'm not sure if it will get the ECC parity information and sector addresses you are after as this information wraps the sector.

    I believe dd will just pull the information from the/a sector it is currently looking at without the header and parity information. (I am open to correction here though).

    Also, will my ability to do this be affected by the type of file system I use? e.g., a journaling file system or otherwise?

    Thanks!

    Mag
    If you can find a tool to do the job your require then it should be file system independent as this is at a very low level indeed on the platters and is the information that wraps the sectors telling the drives firmware where the sectors are and the ECC checksum for error correction.

    I'm intrigued and i am also Googling to see if there is some software you can use under Linux.

    I'll post back if i find any.

    Kind regards
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  3. #3
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    Mar 2013
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    Re: Read the header of a disk sector

    Hi Matt,

    Thanks for your input and your welcome.

    I've been doing some searching (and have been experiencing a pretty steep learning curve), and finally found this thread: http://www.forensicfocus.com/Forums/...r=asc/start=7/. The last post pretty much clears up the question. I can't read that data; not unless I were to find drive model-specific software. I was hoping to do something more drive-agnostic.

    I'm wondering, though, if I'll be able to do this with blocks of data...the program badblocks seemed a pretty good start. If I need help I'll start a new thread.

    Thanks!

  4. #4
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    Re: Read the header of a disk sector

    I'm not quite sure what you mean with blocks of data, but I guess dd, or on a lower level, hdparm --read-sector would do the job. axi-cache search also gives me blktool, scsitools and sg3-utils as packages similar in function to hdparm, but I never used them. Yet some tools from sg3-utils like sg_dd and its variants look promising.

  5. #5
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    Mar 2013
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    Re: Read the header of a disk sector

    Hey Schragge, thanks for the ideas. I'll look into them. Don't think that dd will be able to read what I'm looking for, but I wonder if there's some way I can delve into the inner workings of the other tools you mentioned...maybe learn how to write a variation on one of them. (At least I have a couple of junk HDDs lying around.)

    'Blocks of data'...from what I understand, I was referring to the organizational structure of an HDD, where sectors are grouped into blocks. Am I mistaken? I've seen the terms used interchangeably on a couple of related man pages.

    Thanks!

  6. #6
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    Ubuntu 14.04 Trusty Tahr

    Re: Read the header of a disk sector

    Sectors are the blocks of data on a drive.
    But drives are organized by types of partitioning, currently MBR(msdos) or gpt(GUID) for most PCs.
    MBR details including 2TiB limit and GPT link
    http://en.wikipedia.org/wiki/Master_boot_record
    Windows does not follow UEFI spec on size of protective MBR (starman's site has a lot of technical detail)
    http://thestarman.pcministry.com/asm/mbr/GPT.htm


    Then within each partition is the format which can be many different types of formats, ext2, ext3, ext4, NTFS etc.

    Not sure what you want to see?
    For info on UEFI boot install & repair:
    http://ubuntuforums.org/showthread.php?t=2147295
    Please use Thread Tools above first post to close thread when/if answered completely.







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