| Q. | What is this page (not) about? | ||
|---|---|---|---|
| A. | Maybe to your disappointment it is not about
video(*). The scope of this page is primarily
computer storage applications of DVD+RW/+R, things like backup,
archiving, data exchange... The downloadable files are an
optional kernel patch and
a couple of user-land utilities dubbed as dvd+rw-tools.
|
| Q. | Kernel patch? This sounds too complicated already! Can't I just use cdrecord or something similar? |
|---|---|
| A. | As for cdrecord[-ProDVD]. DVD+RW/+R recording strategy is somewhat different from one supported by cdrecord, so it simply doesn't work (nor do dvdrtools despite what RedHat 7.3 Release Notes say). But do you have to apply the kernel patch? It should be explicitly noted that the user-land utilities, dvd+rw-tools, do provide for burning of DVD+RW/+R without explicit kernel support. So that if they fullfill your requirements, then patching the kernel is by all means optional. |
| Q. | What is the kernel patch good for then? |
|---|---|
| A. | DVD+RW (but not DVD+R) is a true random write access media and therefore is suitable for housing of arbitrary filesystem, e.g. udf, vfat, ext2, etc. This, and this alone, qualifies DVD+RW support for kernel implementation. However! I have to recommend to deploy it with caution, see tutorial for further details. Then support for arbitrary filesystem usfotunately doesn't seem to work with 1st generation drives, Ricoh MP5120A and derivatives (see Technical Ramblings below for further details). |
| Q. | What are the dvd+rw-tools for? |
|---|---|
| A. | As already implied/mentioned to master the DVD+RW/+R media with:-) I could simply refer you to the tutorial, but figured that couple of words about the [original] design ideas behind growisofs, the principal burning utility, wouldn't harm. Even though modified kernel can let you put for example an ext2 filesystem on DVD+RW, it's probably not very practical, because you most likely want to access the data on arbitrary computer. Or in other words you most likely want ISO9660. 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 (yes, DVD+RW has no notion of multiple sessions)? Complete remastering which takes more and more time as dataset grows? Well, yes, unless you employ growisofs! growisofs provides the way to both lay down and grow an ISO9660 filesystem on (as well as to burn an arbitrary pre-mastered image to) both DVD+RW and DVD+R media. |
| Q. | Do I still need cdrtools? |
|---|---|
| A. | Yes. It should be explicitly noted that growisofs is a front-end to mkisofs, i.e. invokes mkisofs to perform the actual ISO9660 filesystem layout. Secondly, the DVD+RW drives available on the market can burn even CD-R[W] media and cdrecord is the tool for this job [and this job only]. |
| Q. | There're dual-format DVD+RW/-RW units available on the market, e.g. SONY DRU500. Can I use dvd+rw-tools with it/them? |
|---|---|
| A. | If the question is if you can use dvd+rw-tools to master the DVD+RW/+R media in a ±RW drive, then the answer always was "definitely yes." If the question really is if you can use dvd+rw-tools to burn even DVD-R[W] media, then I have the pleasure to inform you that as of version 5.0 dvd+rw-tools provide experimental support even for recording of DVD-R[W] media and refer you to a dedicated page for futher details. |
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 yet figured out the way around them. So the status of this "project" is rather "gathering experience" than "ready for production environment."
If you have submitted a problem report and haven't
heard from me within 4-5 working days, then you most likely overlooked
something on the page. Please read it more attentively...
If you have an IDE unit, make sure it is "routed" through ide-scsi emulation layer by either:
options ide-cd ignore=hdX pre-install sg modprobe ide-scsi pre-install sr_mod modprobe ide-scsi pre-install ide-scsi modprobe ide-cd
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.
If you have an external unit, just get it working as CD-ROM first. I myself have no personal experience whatsoever with USB or IEEE1394/Firewire 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 reliably as CD-ROM and 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.
If you're running 2.4.19 or .20, consider applying this drivers/scsi/sg.c patch. I write "consider" and not "do" for the following reasons:
Download, unpack and compile the the toolchain. Note that separate source code files found in the download catalog are provided mainly for references purposes. To build the thing do pick the .tar.gz archive, which contains Makefile as well as .spec file.
If you have 1st generation drive (Ricoh MP5120A and derivatives) do consider upgrading your firmware (see Ricoh, HP, MET pages). Fixed bug descriptions are vague, but at the very least after upgrade to 1.34 I could no longer reproduce infrequent "random positioning errors" when reading 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 reportedly improves compatibility with a number of DVD-ROM drives (more about this matter in Technical Ramblings).
Several 2nd generation unit (Ricoh MP5125A 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.
Formatting the DVD+RW media. Just pass the device name, e.g. /dev/scd0, as an argument to dvd+rw-format. To make formatting process reasonably fast the media gets formatted only partially, as you can notice by observing a progress indicator displayed by the program. 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 are salesman's GB, i.e. 10003 and not 10243.
It was observed that excessive reformats can render media unusable already after 10-20 reformats and [enforced] reformat is therefore not recommended. As you might remember former recommendatations for reformatting were for privacy reason. Version 2.x is not suitable for this purpose, because so called "immediate" form (first utilized in version 2.0) of the "FORMAT UNIT" command does not attempt to zero all the data written so far. If you are concerned about privacy, nullify explicitely with 'growisofs -Z /dev/scdN=/dev/zero' (or 'dd if=/dev/zero of=/dev/scdN bs=32k' if you've patched the kernel and like dd better:-).
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.
Burning with growisofs. There is no manual for growisofs as there is very little need for one. 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, should] consult mkisofs manual page and accompanying reference documention (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 mkisofs command line are:
Otherwise everything that applies to [multisession] 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 "session" with and stick to them, e.g.:
growisofs -Z /dev/scd0 -R -J /some/files growisofs -M /dev/scd0 -R -J /more/files
Oh! Do make sure you have at least mkisofs 1.14 on your $PATH (mkisofs 1.14 is part of cdrtools 1.10).
In addition, growisofs [version 3.3 or 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 filesystem, 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 want to burn output generated by an arbitrary program, you can use:
dumpsomething | growisofs -Z /dev/scd0=/dev/fd/0
Burning DVD+R implies extra limitations:
And once again, do keep in mind that 4.7GB are salesmen's GB, i.e. 10003 and not 10243. If translated to "real" GB, DVD+R[W] 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 accomodate the data-set to be burned, meaning that it was your 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 overriden 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 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 me how. 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 'mkisofs -pad . | dd of=/dev/scdN obs=32k' or even 'mke2fs -b 2048 /dev/scdN' and observe kernel logging "srN: dirty DVD+RW media."
If you have previous patch version applied, then you have to back it out first. The simplest way is probably to restore drivers/scsi/sr*.[ch] and drivers/cdrom/cdrom.c from your original Linux source code ditribution.
Even though kernel now permits to build and mount arbitrary filesystem, 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. Now the thing about fully fledged filesystems 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 filesystem level] would improve the situation, but ideally filesystem driver should definitely refrain from modifying the superblock [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 optimizations. 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 won't work as /dev/raw expects specifically aligned buffer... Good news are that sdd aligns the transfer buffer so that if you've got an image to burn down (or want to nullify) stick to 'sdd of=/dev/raw/rawX obs=32k ...'
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 rewritable/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 "happy," make sure that at least 1GB is written.
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 disk 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 should not be affected by this operation. "Should" is a reminder of the project status, "experience gathering." 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.
Then non-finalized DVD+R disks 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 DVD+R disc in a single take and don't plan to use it for multi-sessioning(***), 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 multi-session disks? Something to correct in next firmware update? |
| (**) | The easiest way is to create couple of holey files with 'touch hugeM.void' and 'perl -e 'truncate ("hugeM.void", 0x7ffffffe)'', and finally to 'growisofs -M /dev/scdN ... huge*.void'. The command is bound to fail with "end of medium reached," but that's what you basically want. |
| (***) | E.g. when mastering DVD-Video disk:-) Note that -dvd-video option [passed to mkisofs] 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 explicitely 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 [apparently all except Sony] and a secret vendor-specific command manipulating this "Book Type" field was implemented. So if you fail to mount/play DVD+RW media, you have an option to attempt
dvd+rw-booktype -dvd-rom -media /dev/scdN
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's 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 incompatibilites, 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 apprently 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're 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...
What does "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 filesystem 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 SEQUENSE 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 SEQUENSE 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 circumstanses. At least I failed to reproduce the problem... But it's being looked into...
This one really beats me. Sometimes the unit simply stops writing signalling 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 explicitely 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 timeout value you pass in cdrom_generic_command is simply ignored and timeout is set to precompiled 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_ioct 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).
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. However! When it comes to DVD-R[W] recording you apparently have to choose(*) between
The catch is that the latter is achieved only in Disk-at-once Recording mode which requires: a) prior knowledge of data-set size, b) uninterrupted data-stream (buffer underruns are not tolerated). While the former is defined only in Incremental Recording mode which implies explicit support by player unit(**). DVD+RW/+R in turn is free from this limitation and combine DVD-ROM/-Video compatibility with unconditional buffer underrun protection.
As already mentioned, DVD+RW groove has "addressing information modulated into it." This gives you an advantage of writing 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 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 arbitrary overwrite is never an option if DVD-RW media was recorded in compatible Disc-at-once mode, whole disc blanking is.
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 filesystem, no special modifications to target filesystem driver are [normally] required. Consequently real-time VBR (Variable Bit Rate) Video recording is a 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. Disk-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 claimed that signal from DVD+RW groove (the one essential for recording, not reading) is much stronger which makes it quite resistant to dust, scratches, etc.
| (*) | As specified in Mt. Fuji draft. Note that this document 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. |
| (**) | I'm no longer 100% sure that explicit support is absolutely required... At least linking sectors [if any] are assigned with Logical Block Address so that address space remains contiguous... Meaning that it should be sufficient to lay the filesystem so to say around those holes/linking areas so that player is never asked to actually play them... |
| (***) | DVD "native" blocksize 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. |