Maybe to your disappointment it is not about
video(*). The scope of this page is primarily
computer storage applications of Blu-ray Disc and
DVD±RW/±R, things like backup, archiving, data
exchange... The downloadable files are an optional [and
essentially historical] Linux 2.4
kernel DVD+RW patch and a couple of user-land utilities
dubbed as dvd+rw-tools.
(*)
Though it doesn't mean that you can't burn
DVD-Video discs with dvd+rw-tools. [Unlike Video-CD] DVD-Video
is "molded" 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
content preparation which is beyond the scope of this
page.
Q.
Kernel patch? What would it be good for?
A.
It should be explicitly noted that the user-land
utilities, dvd+rw-tools, do suffice for BD/DVD recording
without explicit kernel support. So if they fulfill your requirements, thenpatching the kernel is by all means optional.
Kernel support would make it possible to house a read-write
file system, e.g. udf, vfat, ext2, etc. and accomodate
"live" data on suitable optical media. However, I have
to recommend to deploy it with caution, see tutorial for further details. Above mentioned
2.4 patch is provided mostly for historical reasons. Linux
kernel version 2.6>=10 is equipped with packet
writing driver which supports even DVD rewritable media,
but I haven't tested it myself, so don't ask:-)
Q.
What are the dvd+rw-tools for?
A.
As implied/already mentioned - to master the Blu-ray Disc and DVD media, both +RW/+R and
-R[W]. I could simply refer to the
tutorial below, but figured that couple of words about the
[original] design ideas behind growisofs, the principal
burning utility, wouldn't harm. Even though a 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 an arbitrary computer.
Or in other words you most likely want ISO9660. The trouble is
that you might as well want to add data now and then.
And what options do you have in the lack of multiple sessions
(no, DVD+RW has no notion of multiple sessions)? Complete
re-mastering which takes more and more time as data set grows?
Well, yes, unless you employ growisofs! Growisofs
provides the way to both lay down and grow an ISO9660
file system on (as well as to burn an arbitrary pre-mastered
image to) all supported optical media.
Q.
But if they support both + and - recording
strategies, why are they called dvd+rw-tools?
A.
For historical/nostalgical reasons, as originally they did
support exclusively DVD+plus. On the other hand now, when the
vast majority of DVD burners that are being introduced to the
market today are DVD+capable, the name most likely refers to
your unit in either case. And you can always consider the plus
in the name as notion of a unique quality, such as
"seamless" multisessioning, not as reference to some
particular format:-)
Yes. It should be explicitly noted that growisofs is a
front-end to mkisofs, 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].
Note that mkisofs is replaced with its successor genisoimage from
cdrkit.
Q.
Does it work with my recorder unit?
A.
If your unit is MMC compliant,
then the answer is "most likely it
just does." Well, as the probability of your unit being
non-MMC compliant is virtually zero, the answer in practice is
unconditionally "most likely."
The [core] tools were reported to work with a wide range of
drives, including [but not limited to]HP
dvd[12345]x0i,Ricoh MP512x,Philips
DVDRW[248]xx,SONY DRU-[157]x0,NEC
ND-[1234]xx0,TDK indiDVD 4x0N,Plextor PX-[57]xx,Benq DW[48]00A,OptoRite DD0[24]0x,Lite-On
LDW-[4816]xxS, as well as nonplus
units such as Pioneer DVR-x0[45679],LG
GxA-40[248]x,Toshiba SD-R[56]112,Panasonic UJ-811, LF-D[35]1x, and not
the least all-mightySW-5582...
Q.
Is there a GUI front-end available for
dvd+rw-tools?
A.
K3b, version 0.10
and later, and nautilus-cd-burner,
version 0.5.1 and later, are both hiding growisofs behind their
pretty buttons and menus:-) Keep in mind that those are not
directly related to dvd+rw-tools development
effort and GUI users should turn elsewhere for end-user
support. Oh! dvd+rw-tools 5.10.x is a minimum requirement for
GUI frontends...
Q.
I don't run Linux. What are my options?
A.
Version 5.4 adds support for OpenBSD/NetBSD.
Version 5.6 adds support for Solaris 2.x [commercial licensing
terms for distribution on Solaris are to be settled with Inserve Technology].
Version 5.8 features FreeBSD
port contributed by Matthew Dillon, FreeBSD Development Team
alumnus. Hewlett-Packard Company has donated
HP-UX 11 support for
5.14(*). IRIX 6.x support appears in
5.19, Win32 one - in 6.0,
while Mac OS X - in 7.0...
¡
Common usage tip!Whenever
separately available [and unless stated otherwise], do use
character-type device entry with dvd+rw-tools,
e.g. OpenBSD/NetBSD users should stick to /dev/rcdXc.
(*)
As of 5.14 HP-UX support was classified as
"initial." Version 5.18 in turn is the one which has
undergone HP quality assurance testing
and is delivered on HP
software depot.
Foreword
As of May 2003 I've decided to advise users to
turn to <cdwrite@other.debian.org>
on support matters. It's an open list, meaning that you don't have
to be subscribed to post
a problem report. List archives can be found at both subscribe page and mail-archive.com.
When submitting report, provide versioning information, exact
command line, exact output generated by the program and
complement it with dvd+rw-mediainfo output for
resulting recording. Do check couple of last archived months, as the
issue might have been discussed recently. If you've chosen to
contact me personally and haven't heard back within a week or so, then
you most likely overlooked something on this page. Please read it more
attentively...
Special thanks for hardware donations [in
chronological order]:
Tutorial
If your burner unit is managed by some
Linux(*) removable media
automounting/autoplaying facility, such as autofs, supermount,
subfs/submount, magicdev, autorun or similar, take it out of its
control! I can't help you with the latter, check your system
documentation (such as google perhaps:-) for specific instructions.
Failure to take your unit out of
Linux(*) automounting/autoplaying facility
control can result in busted recording, a coaster! At the
very least you have to make sure your unit is not automounted during
recordings.
(*)
dvd+rw-tools support Solaris volume manager and
IRIX mediad in more gracious manner and it's safe to leave recorder
under their control.
Remember to consult Hardware Compatibility Notes for possible
caveats or vendor-specific instructions for your unit. Well, such
reminder belongs at the end of tutorial, but I consider it important
enough to bring it up already here:-)
If you have an IDE unit and run 2.4.x
kernel, you most likely want to "route" it through ide-scsi
emulation layer by either:
passing "hdX=ide-scsi"
argument to kernel;
appending following lines to your /etc/modules.conf:
Keep in mind that once hdX
is routed through ide-scsi, you can no longer refer to /dev/hdX(*), but to corresponding
/dev/scdN only.
(*)
well, except as in hdparm -d [0|1] /dev/hdX. As for DMA settings. 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 appears to be specific to
some IDE chipsets...
If you have an external unit, just get
it working as CD-ROM first. I myself have limited experience with USB or IEEE1394/Firewire optical storage
devices and have to direct you elsewhere for specific instructions. I
however am confident that if you manage to get your drive working
reliably as CD-ROMandCD-R[W]
burner, then you won't have any troubles with dvd+rw-tools either. USB
connected drives were reported to be working fine since eternity.
Firewire connected drives in turn were reported to fail miserably under
2.4.18. The failure didn't seem to be DVD recording 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 and later kernels.
If you're running 2.4.19 or .20, consider
applying this drivers/scsi/sg.c patch.
The bug is fixed in .21. I write "consider" and not
"do" for the following reasons:
dvd+rw-tools are not affected by this bug (as they don't use SG_IO
interface), cdrecord [potentially] is;
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;
As of version 5.6 dvd+rw-tools add support for SG_IO
pass-through or in other words support for Linux 2>=5[.43],
where "generic" SCSI interface can be bypassed by issuing
SG_IO ioctl directly against block device, such as /dev/hdX. I wish it worked without need for interim
patches #1 and #2, (the latter is relative to
2.5.69-75, the 1st problem is addressed in .71, 2nd one - .75-bk3 in
"last
minute" prior first 2.6 cut. As for 2.6 in more general sense.
As you can imagine this new interface renders ide-scsi layer
superfluous and "the[ir] official plan™" is to scrap
it. I'm not really fond of the idea, but not for /dev/sg* account. I
mean I [personally] would prefer to keep ide-scsi and use SG_IO
pass-through with /dev/scdN, rather than with
/dev/hdX:-)
If you have to make dvd+rw-tools work under Linux
kernel 2.6.8, then upgrade the tool-chain to 5.21.x or later and
manually reward the installed binaries with set-root-uid flag. But the
"supported" recommendation is to just stay away from this
particular kernel version. As for 2.6>8, dvd+rw-tools 5.21.x is
requirement. Oh! dvd+rw-booktype utility would require set-root-uid
privilege then. Given its semi-official status and the fact that this
utility works only with limited number of units, installation procedure
abstains from installing dvd+rw-booktype set-root-uid, leaving
this security sensitive choice to the end-user.
Download, unpack and compile the the tool-chain. To build the thing do pick the
.tar.gz archive, which contains Makefile as well as .spec file. You
will need both C and C++ compilers installed. Separate
source code files found in the download catalog
are provided mainly for on-line reference purposes (such as revision history:-).
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 native 64-bit ABI (which can normally be done with
'make TARGET_ARCH=-m64'). 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.
As new media products and brands are being
introduced to the market all the time, it apparently pays off to
periodically check for firmware updates. For elder units
firmware update might even be an absolute requirement for using
new media. Special note for HP users. HP no longer posts firmware
updates on a web-page. Instead they let some Windows auto-update gizmo
to pick firmware updates among dvd[1-6]00*.exe
files in their FTP
directory, so that readers of this page tend to miss them...
Formatting the BD and DVD+RW media.
Virgin BD and DVD+RW media needs to be initally formatted prior usage.
Once again, only virgin BD and DVD+RW media needs to be
formatted. 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. /dev/scd0, as an
argument to dvd+rw-format. Though
in BD case it does offer more flexibility than
growisofs. To make formatting process reasonably fast, less than 1
minute, the media gets formatted only partially, as you can notice by
observing 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 transparently, as you add more
data. Oh! Do keep in mind that DVD capacity of 4.7GB is expressed in
salesman's GB, i.e. 10003 and not 10243. And
so is one of BD.
It was observed that excessive reformats can render
DVD+RW 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 re-formatting procedure does not
substitute for blanking. If you want to nullify the media, e.g. for
privacy reasons, do it explicitly with 'growisofs -Z
/dev/scdN=/dev/zero'. Otherwise just
write over previous recording as it simply wasn't there, no
re-formatting is required.
Burning with growisofs. There is hardly a need for
manual for growisofs. In a nutshell growisofs just passes all command
line arguments to genisoimage and dumps its output directly onto the media.
The first part means that you basically can [well, should]
consult genisoimage manual page and
accompanying reference documentation (including multisession 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:-). Differences from genisoimage command line
are:
you may not use -o option;
you don't have to specify -C option, growisofs will construct one
for you;
there is internal -Z option for initial session recording, this
substitutes for originally suggested 'genisoimage | dd of=/dev/scd0';
Otherwise everything that applies to
[multisession] mastering with genisoimage applies to growisofs as well. For
example just like with genisoimage you should make a note on which options
you used to master the initial "session" with and stick to
them, e.g.:
Oh! Do make sure you have genisoimage on your $PATH
(genisoimage is part of cdrkit,
or at least mkisofs 1.14 (mkisofs 1.14 is part of
cdrtools 1.10). If you consider passing /same/files as argument, or in
other words consider deploying growisofs for incremental
multisession backups, then you shall find this '-old-root' extension to
mkisofs 2.0-2.01 simply indispensable.
The idea and implementation by Patrick Ohly is to "graft"
recording sessions as separate directories. Each backup
increment/directory is ment to contain both updated files and
references to previously backed up ones, which facilitates
comparison between increments as well as fine-graded restore.
Number of users asked about opposite to
multisessioning: multivolume support. Being essentially a recording
program growisofs does not support multiple volumes by itself. There're
couple of front-ends I can recommend that arrange for this: scdbackup and
shunt. But back to
growisofs...
In addition to intuitive -Z interpretation,
growisofs [version 3.3 and later] recognizes special form of -Z command
line option which permits burning of arbitrary pre-mastered images. The
"magic" command is:
growisofs -Z /dev/scd0=image.iso
where image.iso represents an arbitrary
object in the file system, such as file, named pipe or device
entry. No, nothing is "growing" here and command name is
counter-intuitive in this particular context. And here is even less
intuitive:-) If you wish to burn down output generated by an
arbitrary program, you can use:
dumpsomething | growisofs -Z /dev/scd0=/dev/fd/0
Burning BD-R/DVD±R implies extra limitations:
Needless to say that you have only one shot with -Z
option:-)
Unlike DVD+RW, DVD±R media does have notion of multiple
sessions. However! Not all legacy units can "see"
beyond the first one. Few DVD-ROM units are capable of DVD-R
multiborder playback, even fewer support DVD+R multisessioning. In
other words your DVD burner might be the only unit in your vicinity
capable to access data added at different occasions.
Even if your DVD unit does "sense" multiple sessions,
Linux kernel [2.4] sometimes fails to pull that information from the
drive:-( Till the problem is looked into and resolved you can
work it around by reloading corresponding driver, most likely
'rmmod sr_mod'.
Linux kernel 2.6<10
users might experience problems
mounting multisession media with last session starting beyond
2.2GB boundary. As fast-acting remedy I can suggest to route your unit
through ide-scsi, the way it was under 2.4. Even though it's declared
unsupported it actually still works in 2.6 (I for one still use it).
And when it comes to DVD+R Double Layer and DVD-R
Dual Layer recordings, growisofs applies yet another limitation,
purely artificial. Taking into consideration Double Layer media prices
growisofs is programmed to refuse to perform unappendable
recordings which are less than 1/2 of blank capacity and to advice
to use single layer media instead.
DVD-R Dual Layer multisessioning is not supported for a reason
discussed on the -RW companion page. Once
again, as of the moment of this writing DVD-R Dual Layer
recordings come out unappendable and can not be grown.
And once again, do keep in mind that 4.7GB are
salesman's GB, i.e. 10003 and not 10243. If
translated to "real" GB, single layer
DVD±R[W] capacity is not larger than 4.4GiB, and BD
- not larger than 23.3GiB! 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 "overburn" condition is not
raised. As of version 5.2 growisofs performs the necessary checks
for you and refuses to start recording if "overburn"
condition appears to be unavoidable. This behaviour can be overridden
with -overburn command-line option.
If you're satisfied with growisofs, then you
should just proceed to the next chapter
and abstain from applying the optional 2.4.x kernel patch. If
you haven't stopped reading beyond this line, download 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 mehow. As you could
have noticed, patch targets SCSI CD-ROM module. This means that you
have to "route" your IDE unit through ide-scsi to get this one
working. To see it in action, insert formatted DVD+RW media and try to
access it, 'dd if=/dev/scdN count=0'
would do. Then verify that kernel logs "srN: mmc-3 profile: 1Ah". You should now be
able to 'genisoimage -pad . | dd of=/dev/scdN
obs=32k' or even 'mke2fs -b 2048 /dev/scdN' and observe kernel logging "srN: dirty DVD+RW media."
Linux 2.6 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 2003, Ricoh MP5240A,
Philips DVDRW416K or BenQ DW400A do not 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).
Even though kernel now
permits to build and mount arbitrary file system, there is one thing you
must keep in mind before you just proceed, no matter how
tempting it might appear.
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 noatime mount option with
DVD+RW media or have it mounted read-only most of the time. However!
Every read-write mount "costs" a super-block update. So that
if you remount the media say 3 times a day, it would last for about a
year [supermount
would exhaust the "budget" way sooner]... Defect management
[in firmware, a.k.a. Mt.Rainier,
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 Linux UDF 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 SourceForge and
build the module separately. Of course you will have to fetch and build
udftools as well. But once it's done just type:
mkudffs --spartable=2 --media-type=cdrw /dev/scdN
mount -o rw,noatime /dev/scdN /mnt/cdrom
mkudffs command line options were suggested
by UDF maintainer, Ben Fennema.
Performance optimization. This paragraph
applies only if you've patched the kernel. As some of you might
remember the original recommendation was "do use obs=32k
for optimal performance." Well, it was rather naive of me to say
so, as common block device layer completely reorganizes the
stream so that '>/dev/scd0' is as good as '|dd
of=/dev/scd0 obs=32k'. 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.
'raw /dev/raw/raw1 /dev/scd0', 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 temporary
workaround, just to get you going so that you can start figuring things
out, consider this
"hacklet"...
Compatibility: caveat lector
This paragraph discusses "DVD-ROM
compatibility," or playability of already recorded media in legacy
units. Blank media compatibility issues, or cases such as failure to
start or fulfill recording because of poor media support by burner
firmware, are beyond the current scope. Turn to your vendor for list of
supported media and/or to the public to share your
experience.
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 terms]. Some units slide the head to
30mm [radial] to calibrate, some to 35mm. In order to keep such players
"happy," make sure that at least 1GB is written [before you
attempt to mount it in DVD-ROM unit].
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
dvd+rw-format -lead-out /dev/scdN
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 is not affected by this operation.
Then non-finalized DVD+R and Sequential
DVD-R[W] discs don't have lead-out either(*).
If you fail to mount/play DVD+R media and wish to sacrifice the
remaining space for immediate compatibility, just fill the media
up(**). Alternatively if you master volume in a single take
and don't plan to use it for multisessioning(***), you have
the option to invoke growisofs with -dvd-compat option and cut
the real lead-out directly after the first session.
(*)
Well, there are lead-outs at the session edges, but
the problem is that "End Physical Sector Number of Data Area"
field in "Control Data Zone" 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 multisession discs...
(**)
But beware the 4GB limit!
If 4GB is already an issue, or if you don't feel like throwing
unrelated data on the media in question, then invoke 'growisofs
-M /dev/scd0=/dev/zero' (supported by 5.6 and later).
Alternative is to re-master the whole volume, naturally with
-dvd-compat option.
(***)
E.g. when mastering DVD-Video disc:-) Note that
-dvd-video option [passed to genisoimage] engages
-dvd-compat automatically.
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 "Book Type" field in "Control Data
Zone" 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 "virtually all players."
This deficiency was recognized by practically all DVD+RW vendors [well,
apparently by "traditional" DVD+RW vendors and not
"latest generation" vendors such as Sony, NEC, TDK...] and a
secret vendor-specific command
manipulating this "Book Type" field was implemented. So if
you fail to mount/play DVD+RW media, you might have an option to
dvd+rw-booktype -dvd-rom -media /dev/scdN
Once again. Not all vendors support this and you
can't expect this utility to work with all recorders.
It's naturally not possible to manipulate the
"Book Type" 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 in advance:
dvd+rw-booktype -dvd-rom -unit+r /dev/scdN
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 "Compatibility
Bitsettings" article at dvdplusrw.org.
There [potentially] are other logical
DVD+RW(*) format incompatibilities, but the "Book
Type" issue discussed above is the only one "officially"
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 DVD Forum(**).
(*)
Finalized DVD+R media branded with
DVD-ROM "Book Type" is virtually identical to
DVD-ROM.
(**)
To which I say "so what?" 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.
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 "they claim," 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...
Technical Ramblings
As for multisession ISO9660 [DVD]
recordings! Unfortunately, Linux ISOFS implementation had 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(*) 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:-( It should be noted that in
reality it's a bit better than it looks on the picture, as genisoimage
collects all the directories in the beginning of any particular session
(there normally are no blues between greens). The first session
is therefore never subject to i-node wrap-around, but not the
subsequent ones! Once again, files
themselves may reside beyond the 4GB
boundary, but not the directories, in
particular not in further sessions. Having noted that directory entries
are actually specified to start at even offsets, I figured that
it's perfectly possible to
"stretch" the limit to 8GB. But in order to assure
maximum interoperability, you should not let any session
start past 4GB minus space required for directory
structures, 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 append
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 guarantee that you can't suffer
from i-node wrap-around. Interim fs/isofs 2.4
kernel patch was addressed to those who have actually ran into the
problem and have to salvage the data. Even though permanent solution
for this problem appears in Linux kernel 2.6.8 (thanks to Paul Serice
effort), growisofs keeps checking for this 4GB limit in order to ensure
broader compatibility of final DVD recordings. This check is not
performed for Blu-ray Disc recordings, as probability that a member of
such user community would run something elder than 2.6.9 is considered
diminishingly low.
(*)
i-node is a number uniquely identifying a single
file in a file system
(**)
well, as DVD+R Double Layer support was introduced
in 5.20, -use-the-force-luke=4gms option was added to override
this behaviour (naturally recommended for Linux kernel 2.6>=8 users and
kernel developers only;-)
Why media reload is performed after every
recording with growisofs? Well, it's performed only if you didn't
patch the kernel:-) But no, I do not insist on patching the kernel!
All I'm saying is that in the lack of kernel support, media reload is
performed for the following reasons. 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 bypasses 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 when flushing the block cache is not an option, e.g. only
privileged user is allowed to perform it. Second reason is to force
kernel to readjust last addressable block in case it was changed as
result of recording. This is done to preclude spurious "attempts to
access beyond end of device."
What does [kernel] "DVD+RW support"
really mean? Even though DVD+RW has no notion of [multiple]
sessions, to ensure compatibility with DVD-ROM it's essential to issue
"CLOSE TRACK/SESSION (5Bh)" MMC 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.
Secondly, whenever you employ fully fledged
file system, I/O requests get inevitably fragmented.
"Fragmented" 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. "Fragmented requests" 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 "COMMAND SEQUENCE ERROR
(2Ch)" ASC. This is the second essential of "DVD+RW
support," namely injecting of "SYNCHRONIZE CACHE (35h)"
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.
Unfortunately the above paragraph doesn't
seem to apply to the 1st generation drives, Ricoh MP5120A and
derivatives:-( "SYNCHRONIZE CACHE (35h)" doesn't
seem to be sufficient and the unit keeps replying with "COMMAND
SEQUENCE ERROR (2Ch)" 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. 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...
Then some [most?] of post-2nd gen units, from
most vendors, seem to not bother about complying with
DVD+RW specification, "true random write with 2KB
granularity" part in particular. Instead they apparently expect
host to apply procedure pretty much equivalent to DVD-RW
Restricted Overwrite. To be more specific host seems to be expected to
coalesce 2KB requests and perform aligned writes at native DVD ECC
blocksize, which is 32KB. Formally this should not be required, but
it's the reality of marketplace:-(
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, "FLUSH
CACHE" might do the trick. Another one is that under
"underrun" condition background formatting kicks off and has
to be explicitly stopped. "Underrun" 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]
-poor-man option (which has to be first in the command line).
This option eliminates request reorders and minimizes possibility for
"underrun" condition (by releasing the pressure off VM
subsystem).
The original idea was to implement DVD+RW support in
drivers/cdrom/cdrom.c. Unfortunately SCSI layer maintains private
"writeable" 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.
Unfortunately it was not possible to implement it
completely in sr_mod.o:-( 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.
Special comment about "what a dirty
hack!!!" 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
"the dirty hack" 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 "quiet" argument instead of modifying
all the calls (too boring).
But even if time-out value passed down to kernel
(with either 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 documented
to be measured in milliseconds... Neither of this holds true! Kernel
treats these values as "jiffies," which is a
platform-dependent value representing time elapsed between timer
interrupts. But if we attempt to send down "jiffies," 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
"jiffy," but didn't care to provide user-land with actual
value (well, not of actual interest, too much legacy code to deal with)
norscale timeouts
accordingly in respect to the legacy value of 10ms.
There is another kernel "deficiency" 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 "TEST UNIT READY"] as
"NO SENSE/LOGICAL UNIT NOT READY/FORMAT IN PROGRESS" sense
bytes but with "GOOD" status. Apparently any sense data with
"GOOD" status is discarded by the common SCSI layer.
It was pointed out to me that DVD+RW units work with
Acard SCSI to IDE bridges.
What does plus in DVD+RW/+R
stand for? Originally this paragraph started as following:
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 "notice" 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 universally playable.
Well, it turned out that I was wrong about one
thing. I failed to recognize that DVD-R[W]
groove also provides for adequately 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
specificaton apparently insists that you choose between
buffer underrun protection and
full DVD-ROM/-Video compatibility.
The specification asserts that 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(*), full DVD-ROM/-Video compatibility is
guaranteed only if recording didn't suffer from buffer underruns. The
problem is that "offended" sectors are denoted with certain
linking chunk appearing as degraded user data, few bytes, which
are supposed to be "corrected away" by ECC
procedure(**). DVD+ splices are in turn only few bits large
and are "accounted" to sync patterns, not to user data
area. 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.
As already mentioned, DVD+ groove has
"addressing information modulated into it," 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(***).
DVD-RW in turn can only be overwritten 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
never an option if DVD-RW media was recorded in [compatible]
Disc-at-once or even Incremental mode, only whole disc blanking is.
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.
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 "guiding" 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...
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 any linking information and is
logically indistinguishable from one written in DVD-R[W] Disc-at-once
mode (or DVD-ROM for that matter).
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.
Now we can also discuss differences between
Double/Dual Layer implementations. DVD+R Double Layer permits for
arbitrary layer break positioning yet maintaining contiguous logical
block addressing. In other words address of the block following the
break is always address of the block preceding one plus 1, even for
arbitrarily positioned break. DVD-R Dual Layer on the
other hand implies unconditionally disjoint logical block addressing
[for arbitrarily positioned layer break that is]. This is because block
addresses as recorded by unit are pre-defined by DVD-dash
groove structure. In practice it means that file system layout has to
effectively have a hole, which "covers" twice the space between chosen
layer break position and outermost edge of the recordable area. And in
even more practical terms this means that mastering programs have to be
explicitly adapted for DVD-R layer break positioning.
Unlike DVD+plus that is.
(*)
According to Mt. Fuji draft
buffer underrun protection is not even an option in DVD-R DAO: "If a
buffer under-run occurs, the logical unit shall stop
writing immediately and the logical unit shall start
writing of Lead-out." Protection is defined in Incremental Sequential
mode and DVD-RW context. By the way, note that earlier versions of this
draft also discuss 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.
(**)
ECC redundancy does permit for more degradation,
more that this linking chunk that is, so that it hadly affects the
playability.
(***)
DVD "native" 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.
