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Old 10-02-2010, 06:37 AM
JD
 
Default size discrepancy

$ ls -l
total 7070588K
-rw-r--r-- 1 jd jd 3616604160 Oct 1 23:27 f14.iso
-rw-r--r-- 1 jd jd 1602 Sep 29 20:35 Fedora-14-Beta-i386-CHECKSUM
-rw-r--r-- 1 jd jd 3616593920 Sep 29 21:56 Fedora-14-Beta-i386-DVD.iso

I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.
One time I used wodim, and 2nd time I used growisofs.
After each burn, I would dd the dvd back in:

dd if=/dev/sr0 of=f14.iso bs=2k

In both cases the size of f14.iso was 10240 bytes larger than
Fedora-14-Beta-i386-DVD.iso.

So, naturally, I will not be able to get the same sha256 sum
as that of Fedora-14-Beta-i386-DVD.iso

So, how do I dd the dvd in and get the same size as original iso?

Perhaps growisofs and wodim are padding during burn.
If that is the case, how do I suppress it?



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Old 10-02-2010, 08:40 AM
Andre Robatino
 
Default size discrepancy

JD <jd1008 <at> gmail.com> writes:

> I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.
> One time I used wodim, and 2nd time I used growisofs.
> After each burn, I would dd the dvd back in:
>
> dd if=/dev/sr0 of=f14.iso bs=2k
>
> In both cases the size of f14.iso was 10240 bytes larger than
> Fedora-14-Beta-i386-DVD.iso.

In general this won't work unless dd is told exactly how much to read off.
Unfortunately, it works often enough that people think it's supposed to. Use the
rawread script from

http://www.troubleshooters.com/linux/coasterless.htm#rawread

instead. This determines the ISO size from the ISO header and then automatically
reads off the right amount.

There is a defect in the Live and netinst images (which started in F12 Alpha,
and only affected i386 and x86_64, not ppc), in that they are larger than the
ISO header indicates:

https://bugzilla.redhat.com/show_bug.cgi?id=585006

To read these off properly, the rawread script won't work, since it assumes that
the ISO header size is correct. Instead, you have to manually compose a dd
command that reads off the size corresponding to the actual ISO file (not the
size in the ISO header).




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Old 10-02-2010, 11:03 AM
Gregory Woodbury
 
Default size discrepancy

On Sat, Oct 2, 2010 at 4:40 AM, Andre Robatino <robatino@fedoraproject.org> wrote:

JD <jd1008 <at> gmail.com> writes:



> I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.

> One time I used wodim, and 2nd time I used growisofs.

> After each burn, I would dd the dvd back in:

>

> dd if=/dev/sr0 *of=f14.iso bs=2k

>

> In both cases the size of f14.iso was 10240 bytes larger than

> Fedora-14-Beta-i386-DVD.iso.



In general this won't work unless dd is told exactly how much to read off.

Unfortunately, it works often enough that people think it's supposed to. Use the

rawread script from



http://www.troubleshooters.com/linux/coasterless.htm#rawread



instead. This determines the ISO size from the ISO header and then automatically

reads off the right amount.



There is a defect in the Live and netinst images (which started in F12 Alpha,

and only affected i386 and x86_64, not ppc), in that they are larger than the

ISO header indicates:



https://bugzilla.redhat.com/show_bug.cgi?id=585006



To read these off properly, the rawread script won't work, since it assumes that

the ISO header size is correct. Instead, you have to manually compose a dd

command that reads off the size corresponding to the actual ISO file (not the

size in the ISO header).

One can also tell dd to read by single physical layer sectors using the "bs=2048"
option. This may increase the read time a bit, but generally results in s more consistent

chance of getting the correct size.

--
G.Wolfe Woodbury
*

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Old 10-02-2010, 11:36 AM
Andre Robatino
 
Default size discrepancy

Gregory Woodbury <redwolfe <at> gmail.com> writes:

> One can also tell dd to read by single physical layer sectors using the
"bs=2048"option. This may increase the read time a bit, but generally results in
s more consistent
> chance of getting the correct size.-- G.Wolfe Woodbury*

The rawread script does this - it reads both the block size (normally 2048) and
the block count from the ISO header, and composes a dd command that looks
something like

dd if=/dev/dvd bs=2048 count=1765915 conv=notrunc,noerror

for a 3616593920-byte ISO (assuming the information in the ISO header is
correct, which it currently is for Fedora install DVD and CD images, but not
Live or netinst). JD's original command also used the "bs=2k" option which is
equivalent (but not the count option). The dd man page only documents upper-case
K for 1024, but I tested and lower-case k works the same.




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Old 10-02-2010, 05:33 PM
JD
 
Default size discrepancy

On 10/02/2010 01:40 AM, Andre Robatino wrote:
> JD<jd1008<at> gmail.com> writes:
>
>> I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.
>> One time I used wodim, and 2nd time I used growisofs.
>> After each burn, I would dd the dvd back in:
>>
>> dd if=/dev/sr0 of=f14.iso bs=2k
>>
>> In both cases the size of f14.iso was 10240 bytes larger than
>> Fedora-14-Beta-i386-DVD.iso.
> In general this won't work unless dd is told exactly how much to read off.
> Unfortunately, it works often enough that people think it's supposed to. Use the
> rawread script from
>
> http://www.troubleshooters.com/linux/coasterless.htm#rawread
>
> instead. This determines the ISO size from the ISO header and then automatically
> reads off the right amount.
>
> There is a defect in the Live and netinst images (which started in F12 Alpha,
> and only affected i386 and x86_64, not ppc), in that they are larger than the
> ISO header indicates:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=585006
>
> To read these off properly, the rawread script won't work, since it assumes that
> the ISO header size is correct. Instead, you have to manually compose a dd
> command that reads off the size corresponding to the actual ISO file (not the
> size in the ISO header).
Thank you Andre.
Very good info!!

JD
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Old 10-02-2010, 05:52 PM
JD
 
Default size discrepancy

On 10/02/2010 04:03 AM, Gregory Woodbury wrote:
>
>
> On Sat, Oct 2, 2010 at 4:40 AM, Andre Robatino
> <robatino@fedoraproject.org <mailto:robatino@fedoraproject.org>> wrote:
>
> JD <jd1008 <at> gmail.com <http://gmail.com>> writes:
>
> > I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.
> > One time I used wodim, and 2nd time I used growisofs.
> > After each burn, I would dd the dvd back in:
> >
> > dd if=/dev/sr0 of=f14.iso bs=2k
> >
> > In both cases the size of f14.iso was 10240 bytes larger than
> > Fedora-14-Beta-i386-DVD.iso.
>
> In general this won't work unless dd is told exactly how much to
> read off.
> Unfortunately, it works often enough that people think it's
> supposed to. Use the
> rawread script from
>
> http://www.troubleshooters.com/linux/coasterless.htm#rawread
>
> instead. This determines the ISO size from the ISO header and then
> automatically
> reads off the right amount.
>
> There is a defect in the Live and netinst images (which started in
> F12 Alpha,
> and only affected i386 and x86_64, not ppc), in that they are
> larger than the
> ISO header indicates:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=585006
>
> To read these off properly, the rawread script won't work, since
> it assumes that
> the ISO header size is correct. Instead, you have to manually
> compose a dd
> command that reads off the size corresponding to the actual ISO
> file (not the
> size in the ISO header).
>
>
> One can also tell dd to read by single physical layer sectors using
> the "bs=2048"
> option. This may increase the read time a bit, but generally results
> in s more consistent
> chance of getting the correct size.
>
> --
> G.Wolfe Woodbury
>
So, what block size do you think I am using in my command:
>> dd if=/dev/sr0 of=f14.iso bs=2k
It has no effect. As Andre states, the correct size is in the in the
header info.
The actual physical size on the DVD seems to have been padded by 10240 bytes
(not sure if that is done during dvd burn, or during dvd read),
and the script Andre pointed me (us) to does the right thing.

Thanx again, Andre!

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Old 10-02-2010, 11:40 PM
Tim
 
Default size discrepancy

On Sat, 2010-10-02 at 10:52 -0700, JD wrote:
> The actual physical size on the DVD seems to have been padded by 10240
> bytes (not sure if that is done during dvd burn, or during dvd read),

When one uses features like "burnproof" so that the burning process can
pad out buffer underruns, and keep on burning until more data comes
through, instead of halting, is that transparent to the (later) reading
of the disc, or a likely cause of this sort of problem?

--
[tim@localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored. I
read messages from the public lists.



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Old 10-03-2010, 12:41 AM
JD
 
Default size discrepancy

On 10/02/2010 04:40 PM, Tim wrote:
> On Sat, 2010-10-02 at 10:52 -0700, JD wrote:
>> The actual physical size on the DVD seems to have been padded by 10240
>> bytes (not sure if that is done during dvd burn, or during dvd read),
> When one uses features like "burnproof" so that the burning process can
> pad out buffer underruns, and keep on burning until more data comes
> through, instead of halting, is that transparent to the (later) reading
> of the disc, or a likely cause of this sort of problem?
>
I have no idea because I did not enable burnproof option, nor overburn.
I was under the impression that the -pad option was for burning audio
CD's only.
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Old 10-03-2010, 11:09 AM
Andre Robatino
 
Default size discrepancy

Tim <ignored_mailbox <at> yahoo.com.au> writes:

>
> On Sat, 2010-10-02 at 10:52 -0700, JD wrote:
> > The actual physical size on the DVD seems to have been padded by 10240
> > bytes (not sure if that is done during dvd burn, or during dvd read),
>
> When one uses features like "burnproof" so that the burning process can
> pad out buffer underruns, and keep on burning until more data comes
> through, instead of halting, is that transparent to the (later) reading
> of the disc, or a likely cause of this sort of problem?

Due to the linux readahead bug, which has never been fixed, padding is a Good
Thing (as long as there's a little extra space on the disc to allow it). I
always use the isopad script at

http://ftp.cs.utoronto.ca/pub/hugh/isopad

before using growisofs to burn discs. When using wodim, its -pad option can be
used. (The -pad option for growisofs is not the same and in fact can't be used
when burning an existing ISO file.) The proper way to avoid problems with read
size is to always specify the correct size in the dd command - which the rawhide
script does, assuming the ISO header information is correct, otherwise it has to
be done manually. If the size isn't specified, whether it works is
hardware-dependent.




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Old 10-03-2010, 12:48 PM
Tim
 
Default size discrepancy

Tim:
>> When one uses features like "burnproof" so that the burning process can
>> pad out buffer underruns, and keep on burning until more data comes
>> through, instead of halting, is that transparent to the (later) reading
>> of the disc, or a likely cause of this sort of problem?

Andre Robatino:
> Due to the linux readahead bug, which has never been fixed, padding is
> a Good Thing (as long as there's a little extra space on the disc to
> allow it).

I was thinking of the schemes that will insert padding in the middle of
a burn, so the burn process can just keep on going, instead of having to
pause (which a DVD+ disc can do), or abort completely (for media that
can't simply pause burning). Rather than thinking about the end of the
disc padding, so that discs end up with a particular desired size, or
padding so that they don't have random data past the end.

If the burning process had to pad out the middle with say 60 megs of
padding space, that could (a) affect checksumming, and (b) cause you
problems if you expected to read 650 megs of data off a disc by reading
only the *first* 650 megs worth of bits on it. This is presuming that
padding in the middle isn't transparent (i.e. done in a way that isn't
noticeable when the disc is, later on, read).

--
[tim@localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored. I
read messages from the public lists.



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