Re: DVD RAM?

Previously J. Clarke <jclarke.usenet@xxxxxxxxxxxxxxxx> wrote:
Arno Wagner wrote:

Previously J. Clarke <jclarke.usenet@xxxxxxxxxxxxxxxx> wrote:
Arno Wagner wrote:

Previously J. Clarke <jclarke.usenet@xxxxxxxxxxxxxxxx> wrote:
Pete wrote:

Hi

I have read that DVD RAM is a much more reliable media for important
backups. However I cant seem to see any drives that take the media in
their cartridge, only DVD re-writers like the GSA 4167b that mention
DVD RAM but pressumably use the type 4 cartridge with the disk
removed.

Can anyone recommend makes/models that use the disks in their caddies?

You're looking for older SCSI drives. Ebay is your best bet, brands
would be Pioneer or Plasmon (not sure if Plasmon made drives or just
relabelled Pioneer).

The chemistry of DVD-RAM is the same as for DVD-RW, all that is
different is
the formatting. There's no real reason to believe that DVD-RAM will be
any more durable than DVD-RW, its main advantage is
convenience--DVD-RAM is designed for data storage and can be treated
like just another disk without kluges such as packet-writing.

Actually there is a serious advantage: RVD-RAM uses verify on write
and does defect management.

Verify on write doesn't mean that the data is going to be there a year
down
the road when you need it. The big problem with DVD as an archival
storage medium is the stability of the chemistry, not the integrity of
the writing process.

Actually verify on write deos help massively, as it identifies whether
a write was good or not.

For certain values of "massive" perhaps.

Doing it in software is not the same. If
the drive does it, it can use higher standards for successful verifies
than for standard reads.

If the drive has the hardware to do this then what prevents the software
from using it?

The software only gets a good/bad feedback. The drive itself sees
the raw signal before any ECC was used and sees the signal strength.
Therefore the drive can do much more than software.

You are correct that it is not the only thing
that guarantees long-term readability. But chemical stability, once
assured, is not the main reliability problem of optical media.

"Once assured" maybe, but who says that it's assured?

Maybe you should read up on the technology you are talking about?

Dust,

There is a new technology developed for dealing with this, it is called a
"rag".

So, do you clean your disks down to microscopic levels before each
write? Sounds highly impractical to me.

areas gone bad,

And why do they go bad? Because your "assured chemistry" is no such thing.

No. Because there are manufacturing variations, dust, imputities.
Ever asked yourself whu HDDs have defect secors?

vibration, etc. is.

"Vibration"? Vibration removes data from optical media? I've never heard
that one before.

Vibration can cause marginal writes.

For example I had one MOD that
had > 900 reallocated secotrs, because dust got into the cartridge.

Well, now, that's one of the problems with cartridges.

I don't think that deserves an answer.

Write only these would all have been potentially unreadable sectors,
possibly after some time (since the initial write could have been
borderline, but a slight degradation could have made them unreadable).

And what would cause such degradation?

Time?

But the drive identified them on write and made sure that all data
was written well. And at the end that I was informed that that last
write was not successful.

Geez, Nero would have done that for 60 bucks.

No, it could not. See above.

I happen to know that this was dust, since
after cleaning and reformatting the same MOD has worked well and
reliably without significant additional defect sectors for several
yeras now. True, MOD is not quite the same chemistry as DVD-RAM,

MOD does not rely on a chemical change, it relies on a change in the
magnetic properties of a material with temperature. It's no more dependent
on chemistry than a tape or magnetic disk is.

Wrong. It relies of a magnetically induced chemical change. And
BTW MOD, DVD-RAM, DVD-RW are all variations of phase change. The
"chemical" you are probably thinking about is the dyes in the
media that can not be rewritten.

but long-term stability is not really an issue with the chemical
structure if the disk was manufactured according to standard (a
real issue with El Cheapo DVD-RWs!).

To _what_ standard? Does the DVD-RAM standard mandate a given chemistry?

It mandates a specific material, yes. And DVD-RAM is not dye based.

There is A;sp a second thing: MOD/DVD-RAM are factory certified and
have an initial defect list, were the manufacturer found weak
spots with _very_ sensitive equipment. No such certification is
done for DVD-RW.

Well, that's nice, but it still doesn't make the chemistry stable.

There is also a second serious advantage:
The cartridge.

Which protects against scratches but does absolutely nothing to make the
chemistry more stable.

As I said the chemistry is not the issue with DVD-RAM.

Chemistry _is_ the issue. You can have absolutely perfect write and if the
chemistry decides to go to Hell a year down the road you lose the data.
This has been the major problem with DVDs for archival storage right along.
There are chemistries that are supposed to be reliable but no guarantees
that any given media use those chemistries.

Scratches are relatively easy to fix--there's a lot of Lexan there
to work with.

That may be a bit naive. Who has the time to polish their disks?

One only polishes the disk if the disk is damaged. This is an infrequent
occurrence.

Actyally you need to polish before each write, since scratched degrade
the write signal.

And what about dust,

Wipe, blow, or brush it off. Geez.

See above.

fingerprints,

If they cause a problem, you clean them off of course.

See above.

accidentd (drops,

What about them? Unless you roll your chair over it drops generally aren't
an issue.

They are.

not correctly
aclingned in closing drive, ...

If the drive closes at all you open it and reinsert the disk.

It amazes me that you trust the one thing that you can't inspect, the
chemistry, but worry about all this stuff that doesn't usually cause
problems in the real world and is generally easily correctable if it does.

The main real-world benefit of the cartridge IMO is
that it gives you a way to put an easily readable label on a
double-sided DVD-RAM. By the way, the cartridge does little to
protect against spills--first time I saw an optical disk
demonstrated the salesman to his dismay couldn't get the drive to
read it. While he was off in search of techs I idly examined the
cartridge, opened the slider, and found that it was full of several
day old coffee.

Not an issue. Jous clean it off with soap and water. The data is still
there.

After you take the cartridge apart.

Yes, so what?

Further, the cartridge is not required for something to be a DVD-RAM.

Yes, and the stated reliability drops dramatically for the formats
without cartridge, or once a disk has been removed from cartridge.

You trust "the stated reliability"? My respect for you has just dropped a
great deal. If it's mission critical data never trust anybody.

I trust that the stated reliability is an upper bound.

If you want durable random-access media in that capacity range you
would do better to go with magneto-optical.

Agreed. DVD-RAM was intended to be the MOD succesor, but it is not
up to it. I have all my important stuff on 3.5" MODs. Usually two
copies. So far I have not los a single bit in 7 years using
this technology.

Would you have lost any of it without that technology?

1.) Yes.
2.) Backups and archiveing would have been far more work and worry

Uh, copying it to MO _is_ "backups and archiving".

Floppies: About half of my older 3.5" floppies were unreadable
when I backed them up 2-3 years after they were last used.

There is something wrong with your hardware, Arno. You've been having all
of these problems, hard disks crashing right and left, diskettes unreadable
after 3 years, etc. You really need to get to the bottom of it instead of
just accepting that "that's the way it is".

CD-R: First loss after 2 week on a disk that verified fine.
Numerous other losses or parial readabilities. And
a bitch to use.

I don't see cranking up Nero or Roxio and dragging and dropping as being "a
bitch".

CD-RW: Disk that verified fine in the writing drive, but was
unreadable in others. Also see CD-R.

Only one, or multiples? If multiple you've got a rum drive. MO can suffer
the same problem.

3 our of 3 MO drives with zero problems. All in use for years now.
I had the above several times with several different writers.

HDDs: Two deathstars and two fried Fujitsus (the second my
mistake). The deathstars with warning signs to late to
get all data off.

So? If you have to "get the data off" then you aren't serious about your
data.

That is the point. I did not, because I had backup on my MIODs.

Cheap tape (Quic-80): A nightmare. Compares that did not compare.
Tapes that were unreadable after a few weeks.

Well, yeah, that's QIC. Totally worthless for any purpose. Tapes aren't
heavy enough to use for paperweights and aren't strong enough to prop up a
table leg and the drives are too light to work as a doorstop.

I have no experience with professional storage tape, but I
expect it comes on par with MOD for reliability, has not as
long data lifetime (say >10 years) and is far cheaper per byte
and far more expensive per installation.

DLT has at least a 30 year storage life. Not accelerated aging, on the
shelf. For equivalent capacity the cost is about the same as MO. The
thing is a 20 gig enterprise-grade DLT drive that cost $5K new is now
obsolete surplus that you get on ebay for 50 bucks in good working order.
The tapes cost about the same as MO cartridges.

You can go that way, no argument here.

Yes, I would have definitely lost data. Unless I had installed a
rigorous "3-copies and check each every year" regiment for my
backups. In contrast MOD is a "write and forget" technology, that
does not require any drivers or special softwware and will reliably
keep your data/family photos/stuff you care about safe for decades.

How would you like a nice bridge? I've recently come into the possession of
one. If that's not to your taste I also have a ski resort in Iowa and some
nice waterfront property in Louisiana. You find it trustworthy only
because it hasn't bitten you yet. Never, _ever_ trust one copy of
_anything_.

With enough redundancy, I do. For critical stuff, I of course have two
or more copies in different physical locations. After all if the
house burns donw, MODs will not survive either.

(Most vendors say > 50 years, a Phillips engineer told me probably
80 years, but there the acceleraded ageing models were getting
shaky...).

They claim that for DVD-R too. Why do you believe the one and not the
other? Accelerated aging models _are_ shaky until they've been correlated
with reality. Epson got bitten a while back with their archival
inks--seems that there was some common set of conditions that they didn't
allow for in their accelerated aging, and their prints were turning orange
in a matter of weeks for some users.

I trust MOD, because it is a mature technology. And because it is
not mass-market, but professional level. Same reason why claims
for SCSI drives are usually more true than those for IDE drives.
Different culture.

Interesting side note: In Japan MOD is all the rage. Seems people
there have more of a long-term outlook on storing data.

Or they're gadget junkies. The fact that something is the rage in Japan
doesn't make it useful. Remember tamaguchis? Or Aibos? Or totoros?

And they are all gone. MOD is not.

Second side note: In medical imagery, the law here requires the
images to be kept available for 20 years. It seems all the
scanners use MODs for this.

Which is fine, but kind of beside the point when you were defending DVD-RAM
earlier.

Personally the last time I lost data was about 20 years ago. Learned to use
RAID and tape and redundant servers and avoid a technological monoculture
and have little problem. Anything that I really care about is on at least
two servers, sometimes three, in separate locations and using different
operating systems. Lot of hassle you say? Nahh, it's all automated.

I have no issue with that. However not everybody has that possibility.

Arno

P.S.: You should really look up the difference between dye based
media and phase-change media. You should also realise that all
the dust/vibration/whatever issues with optical media are while
writing to them and that is were the verify by the drive makes
all the difference.
.

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