Re: copying files with bad CRCs

Previously yawnmoth <terra1024@xxxxxxxxx> wrote:
Say I wanted to copy a *.avi video file (xvid encoded; it's currently
on a hard drive)) but was told (by Windows XP) I couldn't because it
had a bad CRC. Is there a way I could sorta just copy it in spite of
the bad CRC?

The reason I ask is because xvid (and MPEG1/2/4, in general) is a
rather resiliant format. A single corrupt byte may just mean that one
frame is bad. If every 20th frame is a keyframes (ie. i-frames, or
whatever), this means that only 20 - (frame position) % 20 frames are
bad. If there are 100,000+ frames, having less then 20 bad frames is
fairly insignificant.

Agreed. Matches my experience.

Yet it's significant enough for Windows to deny
you access to the whole file?

The problem here is that the underlying OS functionality
is not prepared to deal with bad CRCs in any way. It can only
report the error.

So, anyway, I think, in some cases, Windows' seeming refusal to let you
do anything with corrupt files is inappropriate. Is there any
work-around that I'm not aware of?

For the defective sector itself, there is not. The disk does not
deliver it to the OS. Some data-recovery siftware may still be
able to do a raw read or the like, but I have no experience
with that. For the rest of the file, there is.

The problem really is not with Windoes, but with the application
that stops to read when encountering a read error.

There is a tool called dd_rescue on Linux, that can serve as an
example. It will skip a 512 byte sector (or other size if set
on the commandline) if it reads bad and continue with the next
sector. It does this on the normal file-access layer and the
approach should work with Windows also.

However, I think that you will either have to programm this yourself
or use Linux dd_rescue to copy the file. Should not be too difficult
to write if you have some programming experience.

Arno

.

Relevant Pages

  • Re: copying files with bad CRCs
    ... had a bad CRC. ... frame is bad. ... CRC errors are not sector errors. ... Depends on what IDE command is issued to the drive. ...
    (comp.sys.ibm.pc.hardware.storage)
  • Re: copying files with bad CRCs
    ... currently on a hard drive)) but was told (by Windows XP) I ... just copy it in spite of the bad CRC? ... If every 20th frame is a keyframes (ie. ... Recovers files from disks with physical damage. ...
    (comp.sys.ibm.pc.hardware.storage)
  • Re: copying files with bad CRCs
    ... had a bad CRC. ... frame is bad. ... A sufficient number of them that the contents can't be repaired by the ECC. ... The problem is that Windows won't give them to you, ...
    (comp.sys.ibm.pc.hardware.storage)
  • Re: copying files with bad CRCs
    ... couldn't because it had a bad CRC. ... frame is bad. ... So, anyway, I think, in some cases, Windows' seeming refusal to let you ... do anything with corrupt files is inappropriate. ...
    (microsoft.public.windowsxp.general)
  • copying files with bad CRCs
    ... couldn't because it had a bad CRC. ... A single corrupt byte may just mean that one ... frame is bad. ... So, anyway, I think, in some cases, Windows' seeming refusal to let you ...
    (microsoft.public.windowsxp.general)