Re: [Dvdrtools-users] DVD+R/+RW support

[Bryan J . Smith]

Volker Kuhlmann wrote:
> Thanks much for your more detailed performance information! I've been
> with DVDs for about 2 years and therefore seem to have missed out on 
> much of your fun ;)

Trust me, it wasn't until the 4th generation DVD+R/+RW that it became 
viable.
I think the proof was in the fact that


> Unfortunately DVD-RAM doesn't have any sort of profile in the market 
> which is worth mentioning,

That is a commonly poor assumption.
DVD-RAM was first.
DVD-RAM will still be around and supported  when DVD+RW and DVD-RW have 
been replaced by BlueRay and others.

> and I know nothing about it

Those who care about longterm backups know all about it.

>  nor how to use it under Linux.

Stick in DVD-RAM disc.
Mount (or let your distro automount it if it does).
As Nextel says ... Done.

Seriously, it's been like that since kernel 2.2.
Once kernel 2.4 distros started coming with udftools, you had to do 0.

It is a generic removable disc from the standpoint of the Linux kernel.
Full GPL support.

>  And darn the media is expensive (and hard to get, most
> shops don't even know what I'm talking about).

It's not a consumer format.

> But we now have 2005. Substandard performance in 2003 and prior surely
> isn't that much of an issue when devising backup strategies now?

"Raw" MO is good maybe 3 years, assuming you don't get an error in the 
original write.
That's the primary problem, only solved by proprietary MO, then PD-CD, 
then DVD-RAM.
There are successors in development, and BlueRay may solve more too.

DVD+RW CAV MO is much better than CD-RW CAV MO was.
I used to call CD-RW CAV as CD+RW to differentiate from CD-RW CLV.
I wish Sony/Philips would have done that when they introduced the first 
10x CD-RW CAV MO drives.

You have to understand how ROM/WORM works compared to MO, which explains 
why CAV MO in a legacy CLV drive or with CLV MO media causes all sorts 
of issues.
But now that DVD-RW CLV MO and DVD+RW CAV MO are not sold as the same, 
there is no issue.

But the lack of a WORM +R really hurts not only its compatibility, but 
longevity.
WORM has about the same write  error rate as magnetic, 10**13.
MO is 10**9, 10000x worse.
That's why DVD-RW and DVD+RW can't be trusted to long-term backup.

DVD-R WORM and DVD-RAM MO are the only standards with longeveity.

> Of course, any organised person verifies burnt disks after burning if
> they're meant for the keeping, and I don't see a difference there
> between +-R(W) or -RAM.

Of course you don't, because you don't know the difference between 
single-groove pressed ROM and recorded WORM.
MO is "pie-slice" so it looks *nothing* like single-grove, hence the 
"emulation" and compatibility issues.
And then there is the longevity issues.

DVD-RAM uses a hardware, real-time verify-after-verify.
It also uses a pre-formatted media that has physical tracking (you'll 
know a DVD-RAM disc from its "clear dashes" when you see it).
The result is an error rate more like WORM, and 100,000 re-writes.

As most people have found, once you write more than a few times with 
CD-RW, DVD-RW or DVD+RW, but lots of files in a FAT/NTFS and even some 
inode filesystems, those 1,000 rewrites easily get eaten up with only 
10-25 full disc rewrites.
And what Sony/Philips doesn't tell you is that DVD+R is really just a 
DVD+RW MO disc that is less tolerant, not a WORM like DVD-R.

MO's pie-slice v. WORM's ROM-like single groove is why DVD+R is not as 
compatible as DVD-R.
Players must know how to emulate the physical layout of MO like WORM, 
and not even many Sony/Philips models did for a long time.

>  I have only once had a verify failure - the
> DVD+RW had a finger print near the outer edge. I wiped it off, and could
> have reburnt the last 500MB with growisofs (cdrecord dvd addons or
> cdrecord-prodvd wouldn't allow to do this), but I was lazy and just
> reburnt the lot. No more errors, and I always use md5sum on the whole 
> filesystem image.

You'd be surprise how many times a MO writes incorrectly, but you don't 
see it until a few reads later.
Or sometimes the memory buffer doesn't actually read from the media.
I used to design verification software that forced a system to read from 
the true media (for missile launch systems).

> Actually, I mostly use ext2. :)

Ext2 is actually one of the better inode filesystems that avoids using 
the same sectors over and over for directory info.
If you are just writing a single tarball, then any inode filesystem will 
be fine.
Of course if you're compressing that tarball, if you get a single byte 
error, any point after it is hosed.

See my 2002 April Sys Admin article about the issues of "double 
archiving" (because ISO/UDF are "archive" formats in themselves).

> Unless you always burn whole disk images. Unfortunately udf is of
> practically unusable performance on Linux, so file-based random access 
> to DVD is a dream for the future, DVD-RAM or otherwise.

UDF works fine for me.
It was really design for DVD-RAM.
I get as sustained 3.8MBps.
Not great, but reliable and no verify is necessary.

> My Pioneer A106 still does very well with 4x media too. Pity it's not
> doing 8x media, not even at 4x, not even properly at 1x (tested with -R
> only though, not +R), pity Pioneer isn't interested in firmware updates,

What software are you using?
There are bugs in dvdrecord that prevent slower speeds on some drives.

> and pity 4x media is disappearing from the market in favour of 8x media.

I have no problem finding 1x and 2x media.

> A106 = becoming expensive paperweight, and I bought it less than 1.5y
> ago. I'm less than impressed.

I have a 4-year-old LF-521 (2x DVD-RAM, 1x DVD-R) series still in use.
No issue with 2x or even 4x DVD-R discs.
But DVD-RAM drives have the most universal lasers.
They are designed for, after all, longterm optical archiving.

The LGs are more consumer drives and I don't expect them to last as long 
as the Matsushita/Panasonic drives.
They also don't take the DVD-RAM cartridges, which are the ultimate for 
archiving.

> Now you're a bit unfair - if you sound like the verbal output of the DVD
> Consortium, the suggestion that you're affiliated with them somehow does
> present itself. ;) Not sure what it has to do with arrogance though.

DVD+R/+RW are arrogant people by nature of not only the arrogant, but 
false advertising of Sony/Philips.
They got HP to license, which drew in MS, and HP quickly wished they 
would not have.
In the financial institutiions I've worked with alongside HP and other 
companies, and they stick with DVD-RAM, not DVD+RW despite HP's own 
product offerings such are clearly "consumer-only."

Most people who bought DVD+RW since 2000 have learned to regret it until 
the 4th gens came out last year.
That's a *lot* of beta testers.
At least DVD-RAM and DVD-R have been consistent since introduction.


--
Bryan J. Smith   mailto:address@hidden
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