CD-RW

[ZIYAD A. M. AL-BATLY]

On Tue, 2005-07-05 at 14:11 +0200, Martin Schmeisser wrote:
> Mustafa Abbasi schrieb:
> > i am curious
> > does the udf filesystem allow you to constantly read and write off a
> > cd-rw.
> > like a small hdd.
> >
> generally, yes
Wrong!  UDF require random access (both read and *write*) of the media
which is impossible with a CD-R, but very possible with a CD-RW (that's
why CD-RW are much expensive than CD-R).

> 
> however it dies have restrictions... for example if you delete a file it
> wont get erased from the disk. thus your space on the disk will shrink
> with time and eventually you have to reformatt it.
You're mixing multi-session CDs with UDF.  They are totally different
subjects.

You can create a file-system (most likely "ISO9660" or what Microsoft
calls it "CDFS") on one session but you can't make it span two or more
sessions.  You can create another file-system on another session and the
two file-systems will co-exist happily with each other and you can see
both (or more if there's any other) providing that:
     1. your CD-ROM drive support multi-session CD.  (I have a very old
        CD-ROM that can't see anything beyond the 1st session.)
     2. your Operating System support and understand multi-session CDs.
One last thing about this:  When you create a new session with a file
with the same name and location as another file already exist on a
previous session, it will appears as if the old file get over-written,
while in fact it still exist on the old session.  All you need to get
the old file is to know on which session it's (the number of the
session) and use the "session=number_of_session" option with "mount".

UDF, on the other hand, is a file-system created specifically to resolve
this issue with CDs.  However, it require read/write access to random
areas of the media (just like any other file-system with write
capability).

> 
> but it's a cool system that i frequently use to get stuff to and from my
> friends
> 
> cheers, Martin
> 
I hope this clears thing for you.
Thanks for sharing.
Ziyad.