Re: Why is the DVD image so large?

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


> 3. no electronics parts = immune to esd / emp like ssd.
> 4. long life time far exceeding hdd/ssd (i.e. hard coat, or mdisk).
> 5. small and light.
> 
> -- 
> CeDeROM, SQ7MHZ, http://www.tomek.cedro.info


-- 
Tomoaki AOKI    <junchoon@dec.sakura.ne.jp>