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Re: Issues brining BD disks from the command line - write failures

On Thu 09 May 2013 01:43:35 NZST +1200, Thomas Schmitt wrote:

>   Let dd copy the computed number of blocks from medium to /dev/null:
>     dd if=/dev/sr1 bs=2048 count=1700758 of=/dev/null
>   If this ends by an i/o error (often near the end of the medium)
>   then the burn was not successful.

Or you could be dealing with a stupid Linux kernel that hasn't got fixed
for the last 15 years. If the recording ends at the end of the
filesystem (common, for obvious reasons) and the size of the filesystem
is not a multiple of some internal Linux buffer size, the last buffer
Linux tries to read is incomplete and gets treated with an I/O error,
although the only error is that of the programmer trying to read past
the end of the legimitate recording.

The workaround is to turn off read-ahead for this test, and perhaps DMA
as well. Easy with hdparm, but that's no use no more, and sdparm doesn't
seem to do it.

The other good thing to do with Linux is to append 2MByte of zeros at
the end of the filesystem and burning that with it, just to keep the
kernel from falling over itself when reading it later.


Volker Kuhlmann                 is list0570 with the domain in header.
http://volker.dnsalias.net/     Please do not CC list postings to me.

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