[KLUG Members] Re: Backup solution -- CD-R/ISO9660, CD-RW/UDF, DVD/UDF

[Bryan-TheBS-Smith]

Scott Thurmond wrote:
> I think my understanding of a cdrw is a bit cloudy.
> For a regular cd once you burn it, it is forever on the cd and you can never
> write to the cd again - even if you only burned a 1K file on the cd.

- CD-R, ISO9660 AND MULTISESSION

CD-R (recordable), yes.  Although the ISO9660 has a "multi-session"
standard where you burn more than one session.  Many older drives and
much older software doesn't like it.  I've usually avoided doing such,
but it is possible.

[ Side note:  CD-R[OM] discs are actually spindled like a record, not
sectored like a floppy/hard disk drive platter.  There is an actual
beginning near the middle of the disk and an ending of the track near
the outsides -- one big long track spun around, inside to out -- just
like an old analog record, only inside to out (instead of outside to
in). ]

> Now, a cdr I thought you could write and delete from it all you wanted.
> Is this not correct?

- CD-RW AND UDF

CD-RW (rewritable) is a re-writable media.  Using UDF (Universal Device
Format) as the filesystem (Linux 2.4 comes with it standard, 2.2
requires a driver download), you can re-write several thousand times.  I
haven't tried this with an IDE CD-RW drive and the ide-scsi emulation
layer, but my SCSI CD-RW (and DVD-RAM) drives appear as a sdX SCSI disk
device (and I just put an /etc/fstab entry, with "UDF" as the filesystem
type).

- DVD-R[OM] AND UDF

BTW, UDF is also the filesystem for DVD.  There are two DVD-R types,
A[uthoring] and G[eneral].  The latest, 2nd gen Matushita/Panasonic
DVD-RAM drives now do DVD-R(G), although Pioneer's latest DVD-R/W does
both DVD-R(G) and DVD-R(A) (the original, $10K Panasonic DVD-R drive
only did DVD-R(A)).  I have *NO*IDEA* how you write to them in Linux, or
master the image since I've never used them.

[ Side Note:  Supposedly Pioneer had contracted someone for Linux
support?  And Pansonic's DVD-RAM is recognized as an old PhaseDual (PD)
drive, so maybe it works for DVD-R as well? ]

- DVD REWRITABLES

There are several rewritable DVD standards.  Matushita/Panasonic DVD-RAM
(2.6/4.7GB single-sided disc and 5.2/9.4GB double-sided cartridge),
Sony/Philips DVD-R+W (3.0/4.7GB single-sided disc) and Pioneer DVD-R/W
(4.7GB single-sided disc).

- DVD-RAM:  THE LONGTERM ARCHIVAL STANDARD

DVD-RAM was the original standard, and 2.6/5.2GB (side/double-sided, the
latter is a cartridge) drives first appeared in 1997 (I know, I bought
one ;-).  The new 2nd gen DVD-RAM drives are 4.7/9.4GB, and can do
DVD-R(G) as I mentioned above.  The great thing about DVD-RAM drives is
that their laser wavelength and extensive error correction produces the
most long-term backup media -- and can be re-written hundreds of
thousands of times (and the cartridged-based double sided version helps
keep the dust off).  DVD-RAM was designed by the DVD consortium to be
the new, long-term, standard optical format.

DVD-RAM drives can also read _everything_, DVD-R, DVD-R+W, DVD-R/W,
etc...  Unfortunately, the opposite is not true.  DVD-RAM requires ECC
logic that most non-Matushita/Panasonic/Creative/Toshiba (as a few
others) DVD-ROM drives don't have.  So DVD-RAM discs cannot be read
everywhere, largely most DVD-ROM drives will barf on them (except for
the aforementioned vendors).  DVD-RAM drives also do *NOT* write/rewrite
CD-R/RW, so you must have a separate drive.

The coolest things about DVD-RAM is the logic is PhaseDual (PD)
compatible.  As such, they work "out-of-the-box" in Linux as a generic
SCSI disk (sdX, provided the kernel has the proper device ident -- I've
had to add 1-line hacks before for newer drives).

- DVD-R/W:  THE CONSUMER DRIVE AND MEDIA STANDARD

Pioneer's DVD-R/W drive has a media that is very readable in most
DVD-ROM drives, and virtually all newer drives.  Unfortunately, it can
be rewritten to even less than CD-RW, under a thousand times.  But for
commodity use by users, DVD-R/W is probably a better choice than DVD-RAM
(which is better for long-term storage).  DVD-R/W drives can also
write/rewrite CD-R/RW, so you don't need a separate CD-R/RW drive
(unlike DVD-RAM).  Because of these benefits, DVD-R/W is now recognized
and supported by the DVD consortium as a standard.

Again, I don't know much about Linux support -- but Pioneer supposedly
contracted someone to do it.

- DVD-R+W:  A DYING BASTARD

Sony/Philips broke off from the DVD consortium in 1998 to create a
competing DVD-R+W standard.  They felt DVD-RAM's reliability was
overkill for consumers, and wanted to put CD-R/RW functionality in the
same drive.  The original DVD-R+W was a 3.0GB standard, and didn't
really appear until late 1999/early 2000 -- almost 3 years later than
DVD-RAM, the drives were more expensive, and just as 2nd gen, 4.7/9.4GB
DVD-RAM drives were about to hit.

Although new 2nd gen DVD-R+W drives with 4.7GB capacities are starting
to appear now, Sony/Philips is now coming back to the DVD consortium in
support of Pioneer DVD-R/W.  Espect DVD-R+W to die very shortly, and
they will only be readable in either actual DVD-R+W drives, most
Sony/Philips (or OEM'd) DVD-ROM drives, and, of course, "I can read
anything" DVD-RAM drives.

-- TheBS

-- 
Bryan "TheBS" Smith    mailto:b.j.smith@ieee.org   chat:thebs413
Engineer  AbsoluteValue Systems, Inc.  http://www.linux-wlan.org
President    SmithConcepts, Inc.    http://www.SmithConcepts.com
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