[mythtv-users] OT DVD ripping software

Michael T. Dean mtdean at thirdcontact.com
Fri Apr 24 14:06:48 UTC 2015


On 04/24/2015 09:47 AM, Simon Hobson wrote:
> I realise this is dragging an old thread from the grave ...
>
> On 28 Oct 2014, Stephen Worthington wrote:
>
>> dd does not stop on block errors, or retry errored blocks.  I have a
>> number of bad DVD-R disks, so I just tried dd on one.  This is the
>> result:
>>
>> root at mypvr:/mnt/vid3/video/r/optical disk recovery# dd if=/dev/cdrom
>> of=VD00218.iso
>> dd: error reading â/dev/cdromâ: Input/output error
>> 8917400+0 records in
>> 8917400+0 records out
>> 4565708800 bytes (4.6 GB) copied, 337.086 s, 13.5 MB/s
>> root at mypvr:/mnt/vid3/video/r/optical disk recovery# ls -al VD00218.iso
>> -rw-r--r-- 1 root root 4565708800 Oct 28 14:01 VD00218.iso
>>
>> As you can see, dd copied the DVD to an image file, despite errors. It
>> took around the same time as copying a disk without any errors.  It
>> did give the one final error message, which is easy to miss - I did
>> this time until I looked hard.  I actually did not see the error until
>> I had copied the text and pasted it into this email.
> It must vary between versions of dd, or perhaps it depends on the source ?
>
> Yesterday at work I needed to do a very quick test to see if a hard drive (640G) was OK in a laptop :
>
> # dd if=/dev/sda of=/dev/null bs=1024k
> <loads of console error messages regarding ata1.00>
> dd: reading `/dev/sda': Input/output error
> 20207+1 records in
> 20207+1 records out
> 21189169152 bytes (21GB) copied. 304.573 s, 69.9 MB/s
>
> It most definitely stopped on input device error, and reported as such.

If you want to ignore errors, you should probably use the option 
conv=noerror,sync , which says to ignore read errors and pad the file 
with NULs for the unreadable data (though the sync option, which pads 
the file, doesn't make a lot of sense if you're just writing to 
/dev/null).  That said, dd isn't meant for this, unlike dd-rescue--not 
to say dd-rescue is meant for ripping DVDs, but saying it's meant for 
rescuing data from bad media.

It's quite possible Stephen (or his distro) specifies 
defaults/aliases/... for dd.

Mike


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