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<H1 ALIGN="CENTER"><A HREF="http://www.dvdplusrw.org/">DVD+RW</A>/<A
HREF="#growisofs">+R</A> for Linux</H1>
<H5 ALIGN="CENTER">by &lt;appro@fy.chalmers.se&gt;,
August 2003</H5>
<P><HR>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">What is this page (not) about?</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.<SUP>&nbsp;</SUP>
	<TD>Maybe to your disappointment it is <B>not</B> about
	video<SUP>(*)</SUP>. The scope of this page is primarily
	computer storage applications of DVD&plusmn;RW/&plusmn;R,
	things like backup, archiving, data exchange... The
	downloadable files are an <I>optional</I> <A
	HREF="linux-2.4.patch">Linux 2.4 kernel patch</A> and a couple
	of user-land utilities dubbed as <A
	HREF="tools/">dvd+rw-tools</A>.

	<P><TABLE BORDER="0" ALIGN="LEFT">
	<TR VALIGN="TOP" ALIGN="JUSTIFY">
	<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
	<TD><FONT SIZE="-1">Though it doesn't mean that you can't burn
	DVD-Video discs with dvd+rw-tools. [Unlike Video-CD] DVD-Video
	is &quot;molded&quot; in an ordinary data file system and
	therefore no explicit support by the burning program is
	actually required. In other words it is the DVD-Video
	<I>content preparation</I> which is beyond the scope of this
	page.</FONT></TR>
	</TABLE>
	</TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">Kernel patch? This sounds too complicated
	already! Can't I just use cdrecord?

</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>It should be explicitly noted that the user-land utilities,
	dvd+rw-tools, do provide for DVD recording without explicit
	kernel support. So that if they <A HREF="#tutorial">fulfill
	your requirements</A>, <I>then</I> <B>patching the kernel
	is</B> by all means <B>optional.</B> As for cdrecord. DVD+RW/+R
	recording strategy is somewhat different from one supported by
	cdrecord, so it simply doesn't work (nor does dvdrecord<A
	HREF="http://www.freesoftware.fsf.org/dvdrtools/">,</A>
	despite what <A
	HREF="http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/release-notes/x86/">RedHat
	7.3 Release Notes</A> say).</TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">What is the kernel patch good for then?
</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>DVD+RW (but not DVD+R) is a true random write access media
	and therefore is suitable for housing of an arbitrary file
	system, e.g. <B>udf,</B> vfat, ext2, etc. This, and this alone,
	qualifies DVD+RW support for kernel implementation.
	<I>However!</I> I have to recommend to <B>deploy it with
	caution</B>, see <A HREF="#udf">tutorial</A> for further
	details. Also note that not all OEMs seem to live up to the
	promise of true random write access. As for the moment of this
	writing apparenly only 2nd generation Ricoh-based units (see <A
	HREF="http://www.dvdplusrw.org/">dvdplusrw.org</A> for
	generation listings) equipped with later firmware can sustain
	I/O fragmentation (see Technical Ramblings below for further
	details) and perform <I>reliably</I>.
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">What are the dvd+rw-tools for?</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>As already implied/mentioned to master the DVD+RW/+R
	(well, as well as DVD<A HREF="-RW/">-R[W]</A>!) media with. I
	could simply refer you to the tutorial, but figured that couple
	of words about the [original] design ideas behind <B><A
	HREF="#growisofs">growisofs</A>, the principal burning
	utility,</B> wouldn't harm. Even though modified kernel can let
	you put for example an ext2 file system on DVD+RW, it's
	probably not very practical, because you most likely want to
	access the data on <I>arbitrary</I> computer. Or in other words
	you most likely want ISO9660. Trouble is that you might as well
	want to <I>add</I> data now and then. And what options do you
	have in the lack of multiple sessions (yes, DVD+RW has no
	notion of multiple sessions)? Complete re-mastering which takes
	more and more time as data-set grows? Well, yes, <I>unless</I>
	you employ growisofs! growisofs provides the way to both lay
	down <I>and</I> grow an ISO9660 file system on (as well as to
	burn an arbitrary pre-mastered image to) <B>all supported DVD
	media.</B></TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">Do I still need <A
	HREF="http://www.fokus.fhg.de/research/cc/glone/employees/joerg.schilling/private/cdrecord.html">cdrtools</A>?
</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>Yes. It should be explicitly noted that growisofs is a
	front-end to <B>mkisofs,</B> i.e. invokes mkisofs to perform the
	actual ISO9660 file system layout. Secondly, the DVD burners
	available on the market can burn even CD-R[W] media and
	cdrecord is the tool for this job [and this job only].</TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">There are dual-format DVD+RW/-RW units
	available on the market, e.g. SONY DRU500. Can I use
	dvd+rw-tools with it/them?
</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>If the question is if you can use dvd+rw-tools to master the
	DVD+RW/+R media in a &plusmn;RW drive, then the answer always
	was &quot;definitely yes.&quot; If the question really is if
	<B>you can use dvd+rw-tools to burn even DVD-R[W] media,</B>
	then I have the pleasure to inform you that as of version 5.0
	dvd+rw-tools provide <I>experimental</I> support even for
	recording of DVD-R[W] media and refer you to <A HREF="-RW/">a
	dedicated page</A> for further details.</TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">Does it work with <I>my</I> DVD burner?
</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.	<TD>If your unit is MMC complaint, then the answer is
	&quot;most likely it just does.&quot; Well, as the probability
	of your unit being non-MMC complaint is virtually zero, the
	answer in practice is unconditionally &quot;most likely.&quot;
	The [core] tools were reported to be working with a wide range
	of drives, including [but not limited to] Ricoh MP512x, HP
	dvdx00i, Philips DVDRW[24]xx, SONY DRU-[15]x0, NEC ND-1x00, as
	well as <A HREF="-RW/">non-plus</A> units such as Pioneer
	DVR-x0[456] and LG GMA-40x0...</TR>
</TABLE>

<P><TABLE CELLPADDING=4>
<TR VALIGN="top" ALIGN="justify">
<TH>Q.	<TH ALIGN="left">I don't run Linux. What are my options?
</TR>
<TR VALIGN="top" ALIGN="justify">
<TD>A.<SUP>&nbsp;</SUP>
	<TD>Version 5.4 adds support for <A
	HREF="http://www.mosha.net/05-dvdrw/dvdrw.shtml">OpenBSD</A>/NetBSD<SUP>(*)</SUP>.
	Version 5.6 adds support for Solaris 2.x (commercial licensing
	terms are to be settled with <A
	HREF="http://www.inserve.se/">Inserve Technology</A>). Version
	5.8 features FreeBSD port<SUP>(**)</SUP> contributed by Matthew
	Dillon, FreeBSD Development Team alumnus.

	<P><TABLE BORDER="0" ALIGN="LEFT">
	<TR VALIGN="TOP" ALIGN="JUSTIFY">
	<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
	<TD><FONT SIZE="-1">OpenBSD/NetBSD users should stick to
	<TT>/dev/<FONT COLOR="red">r</FONT>cdXc</TT>!</FONT></TR>
	<TR VALIGN="TOP" ALIGN="JUSTIFY">
	<TD><FONT SIZE="-1"><SUP>(**)</SUP></FONT>
	<TD><FONT SIZE="-1">FreeBSD tip! If you have an IDE unit, <A
	HREF="http://www.cuivre.fr.eu.org/~thomas/atapicam/">atapicam</A>
	is your password! Secondly, if you have <TT>devfs</TT> mounted,
	you might have to <A HREF="fdescfs.sh">mount</A>
	<TT>fdescfs</TT> as well.</FONT></TR>
	</TABLE>
	</TR>
</TABLE>

<P><HR>

<H3>Foreword/Disclaimer</H3>

<P ALIGN="JUSTIFY">Given the absolute lack of [initial] support from
vendor(s) you should consider this page to be a result of guesswork.
There still is a couple of fatal failures indicated by vendor-specific
error codes (see Technical Ramblings) and I didn't <I>yet</I> figured
out the way around them. So the status of this &quot;project&quot; is
rather &quot;gathering experience&quot; than &quot;ready for production
environment.&quot;

<P ALIGN="JUSTIFY">As of May 2003 I've decided to advise users to turn
to &lt;<A
HREF="mailto:cdwrite@other.debian.org">cdwrite@other.debian.org</A>&gt;
on support matters. It's an open list, meaning that you don't have to
be <A HREF="http://lists.debian.org/cdwrite/">subscribed</A> to post a
problem report. List archive can be found <A
HREF="http://www.mail-archive.com/cdwrite%40other.debian.org/">here</A>.
If you've chosen to submit a problem report to me personally and
haven't heard back within 4-5 working days, then you most likely
overlooked something on this page. Please read it more attentively<A
HREF="keys.txt">...</A>

<A NAME="tutorial"><P><HR></A>

<H3>Tutorial</H3>

<P><HR WIDTH="50%" ALIGN="LEFT">

<UL>

<P><LI><P ALIGN="JUSTIFY"><B>If you have an IDE unit,</B> make sure it
is &quot;routed&quot; through ide-scsi emulation layer by either:

<P><UL>
<LI>passing &quot;<TT>hd<FONT COLOR="red">X</FONT>=ide-scsi</TT>&quot;
argument to kernel;
<LI>appending following lines to your /etc/modules.conf:
<BLOCKQUOTE>
<PRE>options ide-cd ignore=hd<FONT COLOR="red">X</FONT>
pre-install sg modprobe ide-scsi
pre-install sr_mod modprobe ide-scsi
pre-install ide-scsi modprobe ide-cd
</PRE></BLOCKQUOTE>
</UL>

<P ALIGN="JUSTIFY">Keep in mind that once hd<FONT COLOR="red">X</FONT>
is routed through ide-scsi, you can no longer refer to <TT>/dev/hd<FONT
COLOR="red">X</FONT></TT><SUP>(*)</SUP>, but to corresponding
<TT>/dev/scd<FONT COLOR="red">N</FONT></TT> only.

<P><TABLE BORDER="0" WIDTH="95%" ALIGN="CENTER">
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
<TD><FONT SIZE="-1">well, except as in <TT>hdparm -d [0|1] /dev/hd<FONT
COLOR="red">X</FONT></TT>. <B>As for DMA settings.</B> Several users of
NEC[-based] units have reported that their systems crash during DVD
recording. The problem appears to be related to DMA settings, at least
switching it off reportedly helps. The problem might be specific to
some IDE chipsets...</FONT>
</TR>
</TABLE>

<P><LI><P ALIGN="JUSTIFY"><B>If you have an external unit,</B> just get
it working as CD-ROM first. I myself have no personal experience
whatsoever with <A HREF="http://www.linux-usb.org/">USB</A> or <A
HREF="http://www.linux1394.org/">IEEE1394/Firewire</A> storage devices
of any kind and have to direct you elsewhere for specific instructions.
I however am confident that if you manage to get your drive working
<I>reliably</I> as CD-ROM <I>and</I> CD-R[W] burner, then you won't
have any troubles with DVD+RW part. As for the moment of this writing,
USB connected drives were reported to be working fine. Firewire
connected drives in turn were reported to fail miserably under 2.4.18.
The failure didn't seem to be DVD+RW related as it reportedly failed
burning even CD-R media. Firewire support was substantially revamped in
2.4.19, and dvd+rw-tools were reported to work with this kernel.

<P><LI><P ALIGN="JUSTIFY">If your burning unit is under some kind of
<B>removable media automounter</B> control, such as autofs, supermount,
magicdev or similar, take it <B>out</B> of its control! I can't help
you with the latter, check your system documentation (such as google:-)
for specific instructions. At the very least you have to make sure your
unit is not automouted during recordings. <!-- Linux kernel should
have/implement &quot;open for exclusive use,&quot; but it doesn't.
Therefore the trouble... --->

<P><LI><P ALIGN="JUSTIFY">If you're running 2.4.19 or .20, consider
applying <A HREF="sg-2.4.19.patch">this drivers/scsi/sg.c patch</A>.
The bug is fixed in .21. I write &quot;consider&quot; and not
&quot;do&quot; for the following reasons:

<P><UL>
<LI>dvd+rw-tools are not affected by this bug (as they don't use SG_IO
interface), cdrecord [potentially] is;
<LI>I however haven't actually experienced the problem with cdrecord
(maybe yet, kernel could have managed to keep buffers neatly aligned
while talking to cdrecord those times I tried), it was VMware that has
failed miserably on me;
</UL>

<P ALIGN="JUSTIFY">As of version 5.6 dvd+rw-tools add support for SG_IO
pass-through or in other words support for Linux&nbsp;2&gt;=5[.43].
Even though the sg bug is present even there, e.g. in <A
HREF="sg-2.5.69.patch">2.5.69</A>, fixed in 2.5.71, dvd+rw-tools are
still not affected by it. As for 2&gt;=5 in more general sense. As you
might know &quot;the[ir] official plan&trade;&quot; is to scrap
ide-scsi.c. The idea is to bypass the real SCSI layer and get SG_IO
working against <TT>/dev/hd<FONT COLOR="red">X</FONT></TT> directly.
Not that I'm fond of the idea, yet I wish it worked without need for <A
HREF="http://marc.theaimsgroup.com/?t=105410790500005&r=1&w=2">interim</A>
patches <A HREF="ide-cd-2.5.69.patch">#1</A> and <A
HREF="ide-cd-2.5.69.+patch">#2</A>, (the latter is relative to
2.5.69-75, the 1st problem is addressed in .71, 2nd one - .75-bk3 in
<A
HREF="http://marc.theaimsgroup.com/?l=linux-kernel&m=105787192005635&w=2">&quot;last
minute&quot;</A> prior first 2.6 cut:-).

<P><LI><P ALIGN="JUSTIFY"><B>Download, unpack and compile the <A
HREF="tools/">the tool-chain</A>.</B> To build the thing do pick the
.tar.gz archive, which contains Makefile as well as .spec file. You
will <B>need both C and C++ compilers</B> installed. Separate
source code files found in the <A HREF="tools/">download catalog</A>
are provided mainly for on-line reference purposes (such as <A
HREF="tools/growisofs.c">revision history</A>:-). 

<P ALIGN="JUSTIFY">If your Linux kernel supports multiple ABIs (e.g.
Linux-sparc64 can run even 32-bit Linux-sparc applications, as well as
Linux-x86_64 can execute legacy 32-bit i386 binaries), make sure you
compile for <I>native</I> 64-bit ABI (which can normally be done with
'<TT>make TARGET_ARCH=-m64</TT>'). The problem here is that 64-bit
kernel has to explicitly convert ioctl structures passed by 32-bit
applications and apparently it does really lousy job when it comes to
CDROM_SEND_PACKET ioctl deployed by dvd+rw-tools.

<P><LI><P ALIGN="JUSTIFY"><B>If you have 1st generation drive</B> (Ricoh
MP5120A and derivatives, see <A
HREF="http://www.dvdplusrw.org/">dvdplusrw.org</A> for generation
listings), do consider upgrading your firmware (see <A
HREF="http://ext.ricoh.co.jp/dvd/asia/support/download/mp5120a/">Ricoh</A>
page for latest version information). Fixed bug descriptions are vague,
but at the very least after upgrade to 1.34 I could no longer reproduce
infrequent &quot;random positioning errors&quot; when <I>reading</I> a
file system with a lot of small files. 1.34 adds support for Verbatim
media and 1.37 apparently for Memorex. Version 1.37 also implements a
secret vendor-specific command which <A HREF="#booktype">reportedly
improves compatibility</A> with a number of DVD-ROM drives (more about
this matter in Technical Ramblings). <!--So for whatever it's worth do
consider upgrading...-->

<P ALIGN="JUSTIFY">Several 2nd generation unit (<A
HREF="http://ext.ricoh.co.jp/dvd/asia/support/download/mp5125a/">Ricoh
MP5125A</A> and derivatives) users have reported that their systems
lock up the while recording DVD+R, but not DVD+RW. I myself have never
experienced anything similar, but firmware upgrade did help those who
has suffered from this. So that apparently even 2nd generation users
should be considering firmware upgrade. Firmware upgrade is actually
required if you want to burn 4x media in your 2nd generation unit.
Well, it will still burn it at 2.4x, but without firmware upgrade you
should expect deplorable results.

<P><LI><P ALIGN="JUSTIFY"><B>Formatting the DVD+RW media.</B> Virgin
DVD+RW media needs to be initally formatted prior usage. Once again,
<B>only virgin DVD+RW media needs to be formatted.</B> As of version
5.10 growisofs detects blanks and applies initial formatting procedure
automatically. Otherwise same effect can be achieved by passing the
device name, e.g. <TT>/dev/scd0</TT>, as an argument to <A
HREF="tools/dvd+rw-format.cpp">dvd+rw-format</A>. To make formatting
process reasonably fast, less than 1 minute, the media gets formatted
only partially, as you can notice by observing a progress indicator
displayed by dvd+rw-format. The final indicator value varies from
firmware to firmware, values as low as 1.6% were observed. But it does
not mean that you can only write that little. The unit keeps formatting
<I>transparently</I>, as you add more data. Oh! Do keep in mind that
DVD capacity of 4.7GB are salesman's&nbsp;GB, i.e. 1000<SUP>3</SUP> and
not 1024<SUP>3</SUP>.

<P ALIGN="JUSTIFY">It was observed that excessive reformats can render
media unusable already after 10-20 reformats. It appears to be a
firmware deficiency, not some common media defect [at least it was
perfectly possible to salvage the media in a unit of different brand],
but I don't recommend [enforced] reformat in either case. Note that
DVD+RW <B>re-formatting procedure does not substitute for blanking.</B>
If you want to nullify the media, e.g. for privacy reasons, do it
explicitly with '<TT>growisofs <NOBR>-Z</NOBR> /dev/scd<FONT
COLOR="red">N</FONT>=/dev/zero</TT>'. Otherwise just write over
previous recording as it simply wasn't there, no re-formatting is
required.

<P ALIGN="JUSTIFY">DVD+R media does not require any formatting
procedure applied and is ready to use out-of-the-box. Apparently, a
reminder that 1st generation units (Ricoh MP5120A and derivatives)
are not capable of burning DVD+R is needed.

<A NAME="growisofs"><P></A><LI><P ALIGN="JUSTIFY"><B>Burning with <A
HREF="tools/growisofs.c">growisofs</A>.</B> There is hardly a need for
manual for growisofs. In a nutshell growisofs just passes all command
line arguments to mkisofs and dumps its output directly onto the media.
The first part means that you basically can [well, <I>should</I>]
consult <A HREF="mkisofs.8.html">mkisofs manual page</A> and
accompanying reference documentation (including multi-session related
section[s]) and the second part means that you shouldn't expect an
ISO-image on the standard output (nor make sure you have enough free
temporary storage<TT>:-)</TT>. Differences from mkisofs command line
are:

<P><UL>
<LI>you may not use -o option;
<LI>you don't have to specify -C option, growisofs will construct one
for you;
<LI>there is internal -Z option for initial session recording, this
substitutes for originally suggested 'mkisofs | dd of=/dev/scd0';
</UL>

<P ALIGN="JUSTIFY">Otherwise <I>everything</I> that applies to
[multi-session] mastering with mkisofs applies to growisofs as well. For
example just like with mkisofs you should make a note on which options
you used to master the initial &quot;session&quot; with and stick to
them, e.g.:

<P><BLOCKQUOTE><PRE>
growisofs -Z /dev/scd0 <FONT COLOR="red">-R -J</FONT> /some/files
growisofs -M /dev/scd0 <FONT COLOR="red">-R -J</FONT> /more/files
</PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">Oh! Do make sure you have at least mkisofs <FONT
COLOR="red">1.14</FONT> on your $PATH (mkisofs 1.14 is part of cdrtools
1.10). If you consider passing <TT>/same/files</TT> as argument, or in
other words consider deploying growisofs for <I>incremental</I>
multi-session backups, then you shall find <A
HREF="mkisofs-2.01a16-root.diff">this '-old-root' extension</A> to
mkisofs <FONT COLOR="red">2<A
HREF="mkisofs-2.0-root.diff">.</A>0-2.01</FONT> simply indispensable.
The idea and implementation by <A
HREF="http://home.pages.de/~ohly/#mkisofs-root">Patrick Ohly</A> is to
&quot;graft&quot; recording sessions as separate directories. Each
backup increment/directory is ment to contain both updated files and
<I>references</I> to previously backed up ones, which facilitates
comparison between increments as well as fine-graded restore.

<P ALIGN="JUSTIFY"><B>In addition to intuitive -Z interpretation,</B>
growisofs [version 3.3 and later] recognizes special form of -Z command
line option which permits burning of arbitrary pre-mastered images. The
&quot;magic&quot; command is:

<P><BLOCKQUOTE><PRE>
growisofs -Z /dev/scd0<FONT COLOR="red">=</FONT>image.iso
</PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">where <TT>image.iso</TT> represents an <I>arbitrary
object</I> in the file system, such as file, named pipe or device
entry. No, nothing is &quot;growing&quot; here and command name is
counter-intuitive in this particular context. And here is even less
intuitive<TT>:-)</TT> If you wish to burn down output generated by an
arbitrary program, you can use:

<P><BLOCKQUOTE><PRE>
dumpsomething | growisofs -Z /dev/scd0=<FONT COLOR="red">/dev/fd/0</FONT>
</PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">Burning DVD+R implies extra limitations:

<P><UL>

<LI>Needless to say that you have only one shot with -Z
option<TT>:-)</TT>

<!---
<LI>Apparently media needs to be manually reloaded [ejected and pushed
back again] after every burning session (well, if you haven't patched
the kernel that is<TT>:-)</TT>
--->

<LI>Unlike DVD+RW, DVD+R media does have notion of multiple sessions.
<I>However!</I> DVD-ROM drives can only &quot;see&quot; the first one.
DVD+R burners will be the only ones capable to access the files added
at different occasions.

<LI>Even though DVD+R unit does &quot;sense&quot; multiple sessions,
Linux sometimes fails to pull that information from the
drive<TT>:-(</TT> Till the problem is looked into and resolved you can
work it around by reloading driver with '<TT>rmmod sr_mod</TT>'.

<LI>If you go for DVD+R multi-sessioning, you have to use mkisofs from <A
HREF="ftp://ftp.berlios.de/pub/cdrecord/">cdrtools-2.0 or later</A> or
apply <A HREF="multi.diff">this patch</A>.
</UL>

<P ALIGN="justify">And once again, do keep in mind that 4.7GB are
salesman's&nbsp;GB, i.e. 1000<SUP>3</SUP> and not 1024<SUP>3</SUP>. If
translated to &quot;real&quot;&nbsp;GB, <NOBR>DVD&plusmn;R[W]</NOBR>
capacity is not larger than 4.4GB! It should also be noted that earlier
growisofs versions did not check if there is enough space on media to
accommodate the data-set to be burned, meaning that it was your sole
responsibility to make sure &quot;overburn&quot; condition is not
raised. As of version&nbsp;5.2 growisofs performs the necessary checks
for you and refuses to start recording if &quot;overburn&quot;
condition appears to be unavoidable. This behaviour can be overridden
with <TT>-overburn</TT> command-line option.

<P><LI><P ALIGN="justify">If you're satisfied with growisofs, then you
should <B>just proceed to <A HREF="#compat">the next chapter</A></B> and
abstain from applying the <B>optional</B> kernel patch. If you haven't
stopped reading beyond this line, <A
HREF="linux-2.4.patch">download</A> the patch, apply it, rebuild  the
kernel or modules and re-install (kernel or cdrom.o and sr_mod.o
modules, whichever appropriate), but don't ask <I>me</I> <A
HREF="http://www.linuxhq.com/patch-howto.html">how</A>. To see it in
action, insert formatted DVD+RW media and try to access it, '<TT>dd
if=/dev/scd<FONT COLOR="red">N</FONT> count=0</TT>' would do. Then
verify that kernel logs &quot;<TT>sr<FONT COLOR="red">N</FONT>: mmc-3
profile: 1Ah</TT>&quot. You should now be able to '<TT>mkisofs -pad . |
dd of=/dev/scd<FONT COLOR="red">N</FONT> obs=32k</TT>' or even
'<TT>mke2fs -b 2048 /dev/scd<FONT COLOR="red">N</FONT></TT>' and
observe kernel logging &quot;<TT>sr<FONT COLOR="red">N</FONT>: dirty
DVD+RW media</TT>.&quot

<!--<P ALIGN="justify">If you have previous patch version applied, then you
have to back it out first. The simplest way is probably to restore
<TT>drivers/scsi/sr*.[ch]</TT> and <TT>drivers/cdrom/cdrom.c</TT> from
your original Linux source code ditribution.-->
	
<P ALIGN="JUSTIFY"><B>Linux 2.6</B> DVD+RW kernel support is planned in
line with DVD+MRW kernel support. This [unfortunately] means that
industry has to deliver a DVD+MRW capable unit first. Yes, the last
sentence means that despite all the promises, there are no such units
available on the market yet. As of the 1st of August, Ricoh MP5240A,
Philips DVDRW416K or BenQ DW400A do <B>not</B> actually implement
Mt.Rainier/EasyWrite support. It remains to be seen if they will offer
it in form of firmware upgrade. In either case, the [original] project
goal is not only read-write support for DVD+[M]RW capable units
themselves, but even playback of DVD+MRW formatted media in legacy
DVD-ROM units (when defect list will be read and interpreted by OS
software in opposite to Mt.Rainier firmware).

<A NAME="udf"><P><LI></A><P ALIGN="justify">Even though kernel now
permits to build and mount arbitrary file system, there is one thing you
<I>must</I> keep in mind before you just proceed, no matter how
tempting it might appear.

<P ALIGN="justify">As you might know DVD+RW media can sustain only
around 1000 overwrites. The thing about fully fledged file systems
is that every read [or tight bunch of 'em] is accompanied by
corresponding i-node update or in other words a write! Now, let's say
you lookup the mount point (e.g. ls /mnt/dvd) ten times a day. This
gives you a 100 days lifetime on your mountpoint and therefore media.
Not really much, huh? So do use <TT>noatime</TT> mount option with
DVD+RW media or have it mounted read-only most of the time. However!
Every read-write mount &quot;costs&quot; a super-block update. So that
if you remount the media say 3 times a day, it would last for about a
year [<A
HREF="http://people.mandrakesoft.com/~quintela/supermount/">supermount</A>
would exhaust the &quot;budget&quot; way sooner]... Defect management
[in firmware, a.k.a. <A
HREF="http://www.licensing.philips.com/information/mtr/">Mt.Rainier</A>,
or at file system level] would improve the situation, but ideally
file system driver should definitely refrain from modifying the
super-block [marking it dirty] if nothing was actually written since
last mount. Given the development status of <A
HREF="http://sourceforge.net/projects/linux-udf/">Linux UDF</A> the
chances for seeing the latter implemented [for UDF] are more than just
conceivable. The request is already filed and even possible solution is
being discussed. But why not give UDF a shot already then? By default
UDF write support is unfortunately disabled and you might have to
reconfigure the kernel and rebuild modules. Alternatively [my preferred
option actually] fetch the code at <A
HREF="http://sourceforge.net/projects/linux-udf/">SourceForge</A> and
build the module separately. Of course you will have to fetch and build
udftools as well. But once it's done just type:

<P><BLOCKQUOTE><PRE>
mkudffs --spartable=2 --media-type=cdrw /dev/scd<FONT COLOR="red">N</FONT>
mount -o rw,noatime /dev/scd<FONT COLOR="red">N</FONT> /mnt/cdrom
</PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY"><TT>mkudffs</TT> command line options were suggested
by UDF maintainer, Ben Fennema.

<P><LI><P ALIGN="JUSTIFY">Performance optimization. This paragraph
applies only if you've patched the kernel. As some of you might
remember the original recommendation was &quot;do use <TT>obs=32k</TT>
for optimal performance.&quot; Well, it was rather naive of me to say
so, as common block device layer <I>completely</I> reorganizes the
stream so that '<TT>&gt;/dev/scd0</TT>' is as good as '<TT>|dd
of=/dev/scd0 obs=32k</TT>'. It should also be noted that dumping to
/dev/scd0 puts quite a pressure on VM subsystem, as the data passes
through block buffer cache. To minimize the pressure and improve
overall system performance bind the cdrom device to a raw device, e.g.
'<TT>raw /dev/raw/raw1 /dev/scd0</TT>', growisofs will locate and use
it automatically. obs=32k makes perfect sense with /dev/raw devices,
but dd (as well as most other programs, e.g. tar) won't work as
/dev/raw expects specifically aligned buffer... As <I>temporary</I>
workaround, just to get you going so that you can start figuring things
out, consider <A
HREF="http://fy.chalmers.se/~appro/LD_*-gallery/index.html?aligned_io#aligned_io">this
&quot;hacklet&quot;</A>...

</UL>

<A NAME="compat"><P><HR></A>

<H3>Compatibility: caveat lector</H3>

<P><HR WIDTH="50%" ALIGN="LEFT">

<P ALIGN="JUSTIFY">In order to optimize seek times DVD[-ROM] players
calibrate their mechanics every time the media is loaded by sliding
the optical head some place, picking up the signal and noting the
physical block address underneath the lens. In order for this procedure
to work with re-writable/recordable media, that particular spot has to
be written to [or de-iced in DVD+RW case]. Some units slide the head to
30mm [radial] to calibrate, some to 35mm. In order to keep such players
&quot;happy,&quot; make sure that at least 1GB is written [before you
attempt to mount it in DVD-ROM unit].

<P ALIGN="JUSTIFY">Other units attempt to seek to lead-out [or vicinity
of it] for calibration purposes. Now the catch is that it's perfectly
possible to produce a DVD+RW disc without lead-out. Most notably media
initially formatted with dvd+rw-format [apparently] doesn't have any
lead-out, not to mention that practically whole surface remains virgin.
If you fail to mount/play DVD+RW media, attempt to

<BLOCKQUOTE><PRE>dvd+rw-format -lead-out /dev/scd<FONT
COLOR="red">N</FONT></PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">which relocates the lead-out next to outermost
written sector as well as makes sure there is no virgin surface before
it. Previously written data should <B>not</B> be affected by this
operation. &quot;Should&quot; is a reminder of the project status,
&quot;experience gathering.&quot; I mean the best I can do is to state
that my hp dvd200i unit doesn't wipe any data when relocating the
lead-out.

<P ALIGN="JUSTIFY">Then non-finalized DVD+R discs don't have lead-out
either<SUP>(*)</SUP>. If you fail to mount/play DVD+R media and wish to
sacrifice the remaining space for immediate compatibility, just fill
the media up<SUP>(**)</SUP>. Alternatively if you master DVD+R disc in
a single take and don't plan to use it for
multi-sessioning<SUP>(***)</SUP>, you have the option to invoke
growisofs with <TT>-dvd-compat</TT> option and cut the real lead-out
directly after the first session.

<P>
<TABLE BORDER="0" WIDTH="95%" ALIGN="CENTER">
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
<TD><FONT SIZE="-1">Well, there are lead-outs at the session edges, but
the problem is that &quot;End Physical Sector Number of Data Area&quot;
field in &quot;Control Data Zone&quot; of the lead-in contains address
of the largest media sector, which makes affected DVD[-ROM] players
calibrate at the outermost edge instead of the first session. Actually
I fail to understand why don't they burn the address of last sector of
the first session in the lead-in even on multi-session discs? Something
to correct in next firmware update?
</FONT></TR>

<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(**)</SUP></FONT>
<TD><FONT SIZE="-1">But beware the <A HREF="#isofs4gb">4GB limit</A>!
If 4GB is already an issue, or if you don't feel like throwing
unrelated data on the media in question, then invoke '<TT>growisofs
<FONT COLOR="red">-M</FONT> /dev/scd0<FONT
COLOR="red">=/dev/zero</FONT></TT>' (supported by 5.6 and later).
Alternative is to re-master the whole volume, naturally with
<TT><NOBR>-dvd-compat</NOBR></TT> option.
<!-- then the easiest way is to create couple of holey
files with '<TT>touch huge<FONT COLOR="red">M</FONT>.void</TT>' and
'<TT>perl -e 'truncate (&quot;huge<FONT
COLOR="red">M</FONT>.void&quot;, 0x7ffffffe)'</TT>', and finally to
'<TT>growisofs -overburn -M /dev/scd<FONT COLOR="red">N</FONT> ...
huge*.void</TT>'. Otherwise you might have to re-master the volume with
<TT>-dvd-compat</TT> option.--></FONT></TR>

<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(***)</SUP></FONT>
<TD><FONT SIZE="-1">E.g. when mastering DVD-Video disc:-) Note that
<TT>-dvd-video</TT> option [passed to mkisofs] engages
<TT>-dvd-compat</TT> automatically.</FONT></TR>
</TABLE>

<A NAME="booktype"><P><HR WIDTH="50%" ALIGN="LEFT"></A>

<P ALIGN="JUSTIFY">Then we have logical format compatibility
issue(s). Probably the very ground for all the controversy around
DVD+RW, rather around DVD+RW media not being playable in a whole range
of players. DVD+RW Alliance was keen to blame on DVD-ROM vendors, even
claiming that they deliberately block playback. But the fact is that
format specifications don't explicitly say that unrecognized format
[designated by &quot;Book Type&quot; field in &quot;Control Data
Zone&quot; of the lead-in] should be treated as DVD-ROM and [in my
opinion] it was rather naive of them to claim and expect that the media
will be playable in &quot;virtually all players.&quot; This deficiency
was recognized by practically all DVD+RW vendors [well, apparently by
&quot;traditional&quot; DVD+RW vendors and not &quot;latest
generation&quot; vendors such as Sony, NEC, TDK...] and a <A
HREF="tools/dvd+rw-booktype.cpp">secret</A> vendor-specific command
manipulating this &quot;Book Type&quot; field was implemented. So if
you fail to mount/play DVD+RW media, you <I>might</I> have an option to

<BLOCKQUOTE><PRE>dvd+rw-booktype -dvd-rom -media /dev/scd<FONT
COLOR="red">N</FONT></PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">Once again. Not all vendors support this and you
shouldn't expect this utility to work with all recorders.

<P ALIGN="JUSTIFY">It's naturally not possible to manipulate the
&quot;Book Type&quot; field on DVD+R media, that is not after the
lead-in is written [which takes place at the moment the first session
gets closed]. But it might be possible to control how it [lead-in] is
going to be branded by programming the drive <I>in advance</I>:

<BLOCKQUOTE><PRE>dvd+rw-booktype -dvd-rom -unit+r /dev/scd<FONT
COLOR="red">N</FONT></PRE></BLOCKQUOTE>

<P ALIGN="JUSTIFY">Meaning that if you fail to play DVD+R media, you
can attempt to burn another disc with more appropriate unit settings.
For more background information about dvd+rw-booktype, see <A
HREF="http://www.dvdplusrw.org/resources/bitsettings.html">&quot;Compatibility
Bitsettings&quot; article at dvdplusrw.org</A>.

<P ALIGN="JUSTIFY">There [potentially] are other logical
DVD+RW<SUP>(*)</SUP> format incompatibilities, but the &quot;Book
Type&quot; issue discussed above is the only one &quot;officially&quot;
recognized. Well, it's actually understandable as it's the only one
that can be recognized and addressed by a DVD+RW vendor alone.
Recognition of other incompatibilities would require cooperation from
DVD[-ROM] player vendors and that's something they apparently are not
willing to show referring to the fact that DVD+RW format is not
approved [and apparently never will be] by <A
HREF="http://www.dvdforum.org/">DVD Forum</A><SUP>(**)</SUP>.

<P>
<TABLE BORDER="0" WIDTH="95%" ALIGN="CENTER">
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
<TD><FONT SIZE="-1">Finalized DVD+R media branded with DVD-ROM
&quot;Book Type&quot; is virtually identical to DVD-ROM.</FONT></TR>
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(**)</SUP></FONT>
<TD><FONT SIZE="-1">To which I say &quot;so what?&quot; DVD Forum is an
alliance of manufacturers just like DVD+RW Alliance is. It [or any
other party for that matter] has no authority to deny a technology
development initiative.</FONT></TR>
</TABLE>

<P><HR WIDTH="50%" ALIGN="LEFT">

<P ALIGN="JUSTIFY">Finally there is a physical incompatibility issue.
They claim that there are optical pick-ups out there not being capable
to decode the track because of low reflectivity of DVD+RW media
surface. I write &quot;they claim,&quot; because in the lack of
cooperation from DVD[-ROM] vendors it's not possible to distinguish
physical from logical format incompatibility, which I find important to
tell apart in order to make sure at least logical format
incompatibility issues don't persist over time. It might be as trivial
as following. As you surely know [already], DVD+RW has same
reflectivity as dual-layer DVD-ROM. Now the catch is that the linear
pit density in turn is same as of single-layer one. Meaning that if
player makes assumptions about linear pit density based on
reflectivity, then it won't be able to trace the track... But either
way, there is very little you can do about this one, but to try another
player...

<P><HR>

<H3>Technical Ramblings</H3>

<P><HR WIDTH="50%" ALIGN="LEFT">

<A NAME="isofs4gb"><P><IMG SRC="isofs4gb.gif" WIDTH=144 HEIGHT=315
ALIGN="RIGHT"></A>

<P ALIGN="JUSTIFY"><B>As for multi-session ISO9660 [DVD]
recordings!</B> Unfortunately, Linux ISOFS implementation has certain
deficiency which limits interoperability of such recordings. In order
to understand it, have a look at sample ISO9660 layout to the right...
Now, the problem is that isofs i-nodes<SUP>(*)</SUP> are 32 bits wide
(on a 32-bit Linux) and represent offsets of corresponding directory
entries (light-greens), byte offsets from the beginning of media. This
means that no directory (green areas) may cross 4GB boundary without
being effectively corrupted<TT>:-(</TT> It should be noted that in
reality it's a bit better than it looks on the picture, as mkisofs
collects all the directories in the beginning of any particular session
(there normally are no blues between greens). The <I>first</I> session
is therefore never subject to i-node wrap-around, but not the
<I>subsequent</I> ones! Once again, <FONT COLOR="blue">files</FONT>
themselves may reside beyond the <FONT COLOR="brown">4GB</FONT>
boundary, but not <FONT COLOR="green">the directories</FONT>, in
particular not in further sessions. Having noted that directory entries
are actually <I>specified</I> to start at even offsets, I figured that
it's <A HREF="isofs-2.4.patch">perfectly possible</A> to
&quot;stretch&quot; the limit to 8GB. But in order to <I>assure</I> the
maximum interoperability, you should <B>not let any session
<I>start</I> past 4GB minus space required for directory
structures</B>, e.g. if the last session is to fill the media up, it
has to be >400MB. As of version 5.3 growisofs refuses to <I>append</I>
a new session beyond 4GB-40MB limit, where 40MB is pretty much
arbitrary chosen large value, large for directory catalogs that is. Yet
it doesn't actually <I>guarantee</I> that you can't suffer from i-node
wrap-around. The <A HREF="isofs-2.4.patch">fs/isofs kernel patch</A> is
addressed to those who have actually ran into the problem and have to
salvage the data.

<TABLE BORDER="0" WIDTH="95%" ALIGN="CENTER">
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
<TD><FONT SIZE="-1">i-node is a number uniquely identifying a single
file in a file system
</FONT></TR>
</TABLE>

<P><BR>

<P ALIGN="JUSTIFY"><B>Why media reload is performed after every
recording with growisofs?</B> Well, it's performed only if you didn't
patch the kernel:-) But no, I'm not insisting on patching the kernel!
All I'm saying is that in the lack of kernel support, media reload is
performed for the following reason. In order to optimize file access
kernel maintains so called block cache, so that repetitive requests for
same data are met directly from memory and don't result in multiple
physical I/O. Now the catch is that block cache layer remains totally
unaware of growisofs activities, growisofs <I>bypasses</I> the block
cache. This means that block cache inevitably becomes out of sync,
which in turn might appear to you as corrupted data. Media reload is
performed to flush/resync the block cache.

<P><BR>

<P ALIGN="JUSTIFY"><B>What does [kernel] &quot;DVD+RW support&quot;
<I>really</I> mean?</B> Even though DVD+RW has no notion of [multiple]
sessions, to ensure compatibility with DVD-ROM it's essential to issue
&quot;CLOSE TRACK/SESSION (5Bh)&quot; <A
HREF="http://www.t10.org/scsi-3.htm">MMC</A> command to
terminate/suspend background formatting (if any in progress) whenever
you intend to eject the media or simply stop writing and want better
read performance (e.g. remount file system read-only). This is what the
patch is basically about: noting when/if media was written to and
"finalizing" at unlock door.

<P ALIGN="JUSTIFY"><B>Secondly</B>, whenever you employ fully fledged
file system, I/O requests get inevitably fragmented.
&quot;Fragmented&quot; means following. Even though you can address the
data with 2KB granularity, it [data] is physically laid out in 32KB
chunks. This in turn means that for example writing of 2KB block
involves reading of 32KB chunk, replacing corresponding 2KB and writing
down of modified 32KB chunk. &quot;Fragmented requests&quot; are those
that are smaller than 32KB or/and cross the modulus 32KB boundaries. In
order to optimize the process certain caching algorithm is implemented
in unit's firmware. Obviously it can't adequately meet all possible
situations. And so in such unfortunate situations the drive apparently
stops processing I/O requests returning &quot;COMMAND SEQUENCE ERROR
(2Ch)&quot; ASC. This is the second essential of &quot;DVD+RW
support,&quot; namely injecting of &quot;SYNCHRONIZE CACHE (35h)&quot;
MMC command in reply to the error condition in question. The command
flushes the cached buffers which makes it possible to resume the data
flow.

<P ALIGN="JUSTIFY"><B>Unfortunately</B> the above paragraph doesn't
seem to apply to the 1st generation drives, Ricoh MP5120A and
derivatives<TT>:-(</TT> &quot;SYNCHRONIZE CACHE (35h)&quot; doesn't
seem to be sufficient and the unit keeps replying with &quot;COMMAND
SEQUENCE ERROR (2Ch)&quot; going into end-less loop. This makes it
impossible to deploy arbitrary file system. I'm open for
suggestions... Meanwhile the I've chosen to simply suspend I/O till the
media is unmounted.

<P ALIGN="JUSTIFY">Even 2nd gen unit were reported to exhibit similar
[but not the same] behaviour under apparently extremely rare
circumstances. At least I failed to reproduce the problem... The problem
reportedly disappears with firmware upgrade...

<P ALIGN="JUSTIFY">This one really beats me. Sometimes the unit
simply stops writing signaling a vendor specific positioning error,
03h/15h/82h to be specific. Especially if the media is newly formatted.
Couple of work theories. One is that block buffer cache reorders
requests so that they are not sequential anymore, &quot;FLUSH
CACHE&quot; might do the trick. Another one is that under
&quot;underrun&quot; condition background formatting kicks off and has
to be explicitly stopped. &quot;Underrun&quot; is in quotes because
the unit is supposed to handle temporary data stream outages
gracefully. If you run into this (you most likely will), try to
complement growisofs command line with [undocumented]
<TT>-poor-man</TT> option (which has to be first in the command line).
This option eliminates request reorders and minimizes possibility for
&quot;underrun&quot; condition (by releasing the pressure off VM
subsystem).

<P><BR>

<P ALIGN="JUSTIFY">The original idea was to implement DVD+RW support in
drivers/cdrom/cdrom.c. Unfortunately SCSI layer maintains private
&quot;writeable&quot; flag controlling the ability to issue WRITE
commands. The flag is impossible to reach for from the Unified CD-ROM
driver. But why am I talking about SCSI when there are only IDE units
out there (at least for the time being)? Well, as you most likely want
to occasionally burn even CD-R[W] with cdrecord you want it to go
through ide-scsi emulation layer anyway. So I figured that SCSI CD-ROM
driver is the one to aim for even for DVD+RW.

<P ALIGN="JUSTIFY">Unfortunately it was not possible to implement it
completely in sr_mod.o<TT>:-(</TT> Minor drivers/cdrom/cdrom.c
modification was required to sense the media before decision about
whether or not to permit write open. That's because DVD+RW drives are
morphing their behaviour after currently mounted media and it's
essential to identify newly inserted media.

<P ALIGN="JUSTIFY">Special comment about &quot;what a dirty
hack!!!&quot; To my great surprise it turned out that time-out value you
pass in cdrom_generic_command is simply ignored and time-out is set to
pre-compiled value of 30 seconds. Unfortunately it's way too low for
formatting purposes and I had to do something about it. Alternative to
&quot;the dirty hack&quot; was to add another argument to sr_do_ioctl
and modify all the calls to it... I've chosen to take over those 31
unused bits from the &quot;quiet&quot; argument instead of modifying
all the calls (too boring).

<P ALIGN="JUSTIFY">But even if time-out value passed down to kernel
(with <I>either</I> CDROM_SEND_PACKET or SG_IO ioctl) is taken into
consideration, it's apparently not interpreted as user-land code
expects it to. As I figured... There is no documentation on
CDROM_SEND_PACKET, but following the common sense most programmers
(including myself:-) expect it to be interpreted in at least
platform-independent manner, such as milliseconds maybe? SG_IO timeout
in turn is <A
HREF="http://www.torque.net/sg/p/sg_v3_ho.html#AEN215"><I>documented</I></A>
to be measured in milliseconds... Neither of this holds true! Kernel
treats these values as &quot;jiffies,&quot; which is a
<B>platform-dependent</B> value representing time elapsed between timer
interrupts. But if we attempt to send down &quot;jiffies,&quot; it
might turn out wrong too [at least for the moment of this writing]. The
catch is that [IA-32] kernel developers figured it's cool to shorten
&quot;jiffy,&quot; but didn't care to provide user-land with actual
value (well, not of actual interest, too much legacy code to deal with)
<I>nor</I> <A HREF="scsi_ioctl-2.5.69.patch">scale</A> timeouts
accordingly in respect to the legacy value of 10ms.

<P ALIGN="JUSTIFY">There is another kernel &quot;deficiency&quot; I ran
into while working on the (original version of) dvd+rw-format utility.
The drive provides background formatting progress status, but
unfortunately it's impossible to access it. That's because progress
counter is returned [in reply to &quot;TEST UNIT READY&quot;] as
&quot;NO SENSE/LOGICAL UNIT NOT READY/FORMAT IN PROGRESS&quot; sense
bytes but with &quot;GOOD&quot; status. Apparently any sense data with
&quot;GOOD&quot; status is discarded by the common SCSI layer.

<!--
<P ALIGN="JUSTIFY">As you might have noticed the time-out value for
&quot;CLOSE SESSION&quot; is 3000 seconds. Does it really take that
long? It might... Disappointed? Don't be! It might happen <I>only</I>
when <I>reformatting</I> used media. Formatting of the <I>blank</I>
media doesn't take longer than a couple of minutes. <I>Reformatting</I>
in turn takes as long as it takes to nullify whatever you had on the
media which requires corresponding time-outs. But do you <I>have to</I>
reformat? Well, only if media contains sensitive data, the new data-set
is smaller than the current one and (for some reason) will be easier
for potentially rival party to get hold of it (in other words when
there is a risk for sensitive data to get exposed). Another reason is
when you want to reuse the media as a master copy for DVD-ROM
manufacturing and want formatted capacity to reflect data-set size.
Otherwise there is <I>no</I> reason to reformat and as long as you
don't you won't be disappointed with how long does it take to
&quot;finalize&quot; the media.
-->

<P ALIGN="JUSTIFY">It was pointed out to me that DVD+RW units work with
Acard <A HREF="http://www.acard.com/eng/product/scside.html">SCSI to
IDE bridges</A>.

<A NAME="plusvsminus"><P><HR WIDTH="50%" ALIGN="LEFT"></A>

<P ALIGN="JUSTIFY"><B>What does <I>plus</I> in DVD+RW/+R stand for?</B>
Originally this paragraph started as following:

<BLOCKQUOTE><P ALIGN="JUSTIFY">The key feature of DVD+RW/+R media is
high [spatial] frequency wobbled [pre-]groove with addressing
information modulated into it. This makes it possible to resume
interrupted [or deliberately suspended] burning process with accuracy
high enough for DVD[-ROM] player not to &quot;notice&quot; anything at
playback time. Recovery from buffer underrun condition in DVD-RW/-R
case in turn is way less accurate procedure, and the problem is that
the provided accuracy is very much what average player can tolerate.
Now given that both provided and tolerated inaccuracies are
proportional to respectively writing and reading velocities there
basically no guarantee that DVD-RW/-R recording that suffered from
buffer underrun will be <I>universally</I> playable.</BLOCKQUOTE>

<P ALIGN="JUSTIFY">Well, it turned out that I was wrong about one
thing. <!--About projecting CD-R[W] buffer underrun recovery procedure
to DVD-R[W] to be specific.--> I failed to recognize that DVD-R[W]
groove also provides for <I>adequately</I> accurate recovery from
buffer underrun condition/lossless linking. Not as accurate as DVD+RW,
but accurate enough for splices to be playable in virtually any
DVD-ROM/-Video unit. Yet! When it comes to DVD-R[W] recording you
apparently have to choose between

<UL>
<LI>buffer underrun protection and
<LI>full DVD-ROM/-Video compatibility.
</UL>

<P ALIGN="JUSTIFY">The latter is achieved only in Disc-at-once
recording mode and only if data-stream was maintained uninterrupted
throughout whole recording. Once again. Even though most vendors
implement lossless linking in DAO mode<SUP>(*)</SUP>, <I>full</I>
DVD-ROM/-Video compatibility is achieved only if recording didn't
suffer from buffer underruns. The problem is that &quot;offended&quot;
sectors are denoted with certain linking chunk appearing as degraded
<I>user data</I>, few bytes, which are supposed to be &quot;corrected
away&quot; by ECC procedure<SUP>(**)</SUP>. DVD+ splices are in turn
only few bits large and are &quot;accounted&quot; to sync patterns,
<I>not to user data area</I>. So that even if suffered from buffer
underrun, DVD+ sector is logically indistiguishable from DVD-ROM. Which
is why it's commonly referred to that DVD+RW/+R combine DVD-ROM/-Video
compatibility with [unconditional] buffer underrun protection.

<P ALIGN="JUSTIFY">As already mentioned, DVD+ groove has
&quot;addressing information modulated into it,&quot; ADIP (ADress In
Pre-groove). This gives you an advantage of writing DVD+RW in truly
arbitrary order, even to virgin surface and practically instantly
(after ~40 seconds long initial format procedure). In addition, DVD+RW
can be conveniently written to with 2KB granularity<SUP>(***)</SUP>.
DVD-RW in turn can only be <I>overwritten</I> in arbitrary order.
Meaning that it either has to be completely formatted first (it takes
an hour to format 1x media), or initially written to in a sequential
manner. And it should also be noted that block overwrite is
<I>never</I> an option if DVD-RW media was recorded in [compatible]
Disc-at-once or even Incremental mode, only whole disc blanking is.

<P ALIGN="JUSTIFY">Unlike DVD-R[W], DVD+R[W] recordings can be
suspended at any time without any side effects. Consider following
scenario. You have a lot of data coming in [at lower rate], which is to
be recorded into one file. Meanwhile it turns out that you have to
retrieve previously recorded data. This would naturally require
suspention of recording. Most notably in DVD-R [and naturally DVD-RW
Sequential] case it would result in a hole in the file being recorded.
So called linking area, most commonly 32KB gap, has to be introduced.
So that you either have to wait till the file is complete or figure out
how to deal with holey files. Thanks to ADIP, DVD+R recording is
resumed from the very point it was suspended at. In DVD-RW Restricted
Overwrite case no gaps are introduced, but if the media was formatted
only minimally, suspension/resuming procedure has to be applied and it
takes ~40 seconds to perform one. In DVD+RW case, suspension/resuming
is instant regardless media state.

<P ALIGN="JUSTIFY">What does all of the above mean in practice? Well, I
was actually hoping that readers would [be able to] figure it out by
themselves. Apparently a couple of &quot;guiding&quot; words are
needed... It means that it's trivial to employ DVD+RW for housing of
live and arbitrary file system, no special modifications to target file
system driver are required. Real-time VBR (Variable Bit Rate) Video
recordings are children's game.

<P ALIGN="JUSTIFY">Sometimes DVD+RW/+R recording strategy is referred
to as packet writing. I myself am reluctant to call it so (or
TAO/SAO/DAO) for the following reason. Despite the fact that DVD-R[W]
provides for lossless linking (within a packet/extent only),
packets/extents are still denoted with certain linking information
which distinguishes it (recording mode in question) from e.g.
Disc-at-once. Now the point is that written DVD+RW/+R media, rather its
Data Zone, does not contain <I>any</I> linking information and is
logically indistinguishable from one written in DVD-R[W] Disc-at-once
mode (or DVD-ROM for that matter).

<P ALIGN="JUSTIFY">It's maintained that signal from DVD+ groove (the
one essential for recording, not reading) is much stronger, which makes
it quite resistant to dust, scratches, etc. 

<P>
<TABLE BORDER="0" WIDTH="95%" ALIGN="CENTER">
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(*)</SUP></FONT>
<TD><FONT SIZE="-1">According to <A
HREF="ftp://ftp.avc-pioneer.com/Mtfuji5/Spec/">Mt. Fuji draft</A>
buffer underrun protection is not even an option in DVD-R DAO. It's
defined in Incremental Sequential mode and DVD-RW context. By the way,
note that this draft also discusses DVD+RW. You should be aware that
they refer to abandoned version which has very little to do with
DVD+RW/+R implementation being discussed here.</FONT></TR>
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(**)</SUP></FONT>
<TD><FONT SIZE="-1">ECC redundancy does permit for more degradation,
more that this linking chunk that is, so that it hadly affects the
playability.</FONT></TR>
<TR VALIGN="TOP" ALIGN="JUSTIFY">
<TD><FONT SIZE="-1"><SUP>(***)</SUP></FONT>
<TD><FONT SIZE="-1">DVD &quot;native&quot; block size is 32KB, and 2KB
granularity is nothing but a trick, but you're excused from playing it,
i.e. reading 32KB, replacing corresponding 2KB and writing 32KB
back.</FONT></TR>
</TABLE>

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