Re: Why is the DVD image so large?

On Mon, Nov 3, 2025 at 7:22 PM Tomoaki AOKI <junchoon@dec.sakura.ne.jp> wrote:
> On Mon, 3 Nov 2025 18:32:59 +0100
> Tomek CEDRO <tomek@cedro.info> wrote:
>
> > On Mon, Nov 3, 2025 at 6:06 PM Sulev-Madis Silber
> > <freebsd-current-freebsd-org111@ketas.si.pri.ee> wrote:
> > > (..)
> > > the optical disks are most of cases readonly, they could retain data well, could be pressed into permanent disk, would be allowed in high security environments where usb would be not maybe
> > >
> > > i miss the optical use cases here, anyone give me insight?
> >
> > 1. read only / immutable.
>
> Some types of optical disks are re-writable, while most of writable
> optical disks are write-once.
>
> And re-writable disks are roughly categorized into two.
>
>   a) Erase and write for the whole disk at once.
>      (Example: CD-RW and DVD-RW)
>   b) Can read/write just like a HDD.
>      (Example: MO, PD, DVD-RAM)
>
> IIRC, DVD-RAM needed to be formatted and written as UDF,
> while MO and PD were mimic'ing HDD and partitionable.
>
> > 2. no moving parts = immune to mechanical malfunction like hdd.
>
> MO, PD and some of DVD-RAM media are provided as "cartridges"
> and had shutter on access hole.
>   https://en.wikipedia.org/wiki/Magneto-optical_drive
>   https://en.wikipedia.org/wiki/Phase-change_Dual
>   https://en.wikipedia.org/wiki/DVD-RAM

Okay, so I found our local optical disk magician (mr. hocuspocus lol),
and he said "DVD-RAM DL disks never existed. JVC made DVD-RW DL but
they never reached the market". So the easiest way is to just get a
bunch of DVD-R DL double layer one time writable which are easily
available and cheap.. or a BD-RE disk :-)

On the other hand I found this on wikipedia
(https://en.wikipedia.org/wiki/DVD-RAM) about DVD-RAM "Holds more data
when using Double Sided discs than dual-layer DVD+RW and DVD-RW -
9.4GB for DVD-RAM vs 8.5GB for DVD+RW DL and DVD-RW DL". Does that
mean optical disks were also double sided not only double layer? They
had to be swapped by hand just like 5.25' floppies :D

Also I just found and ordered to play around: BD-RE XL (100GB
rewritable Sony disk ~17EUR no enclosure) and DVD-RAM (4.7GB Panasonic
disk ~5EUR no enclosure).. lets see if my recorder firmware supports
them and would it be possible to just mount DVD-RAM and read-write as
standard disk but slow :-P

-- 
CeDeROM, SQ7MHZ, http://www.tomek.cedro.info