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Re: Unidentified subject!

Bill Davidsen <davidsen@tmr.com> wrote:

> > I recommend you to read the documentation from cdrtools to learn that your  
> > claim is not true: cdrecord of course can burn from a pipe. 
> >   
> To be more correct, cdrecord can not burn from a pipe with anything 
> useful writing the pipe, while growisofs can. cdrecord requires that the 

You seem to have an narrow and incorrect sight of the world....

In the same narrow minded manner, I could claim that you cannot
do anythign useful with growisofs (see below.....).

> total size of the data be known before starting, which means that the 
> usual benefits of using a pipe are not possible:
>         * avoid having to write an image to disk when space is tight
>         * allow overlapping of image creation and burning time
>         * allow burning data which changes in size between observation

This is if course not true, see below for more information. 

> So if you can't know the exact size of the image before you start, you 
> can't burn from a pipe. Actually, I don't think you can burn at all with 
> dynamic data, there are old posts here indicating that even using the 
> builtin mkisofs, if the files are growing there can be problems. The 
> final size can be on the command line or in the ISO image, but must be 
> known at the start of the burn. See the man page "isosize" and "tsize=" 
> descriptions. The latter explains that cdrecord uses modes which require 
> the information early.

It seems that you are uninformed - sorry but growisofs uses mkisofs!

Mkisofs is definitely not designed to work on a dataset that changes while
mkisofs is running.

Whether you _believe_ that you have been able to write something useful with
growisofs, while the dataset mkisofs is working on changes, is irrelevent.
In most cases, the resulting DVD will be just unusable or mkisofs will even
_abort_ because a file did change it's size between the creation of the
metadata part of it's output and the time when reading of the related file.

CONCLUSION: growisofs _may_ in some rare cases be able to create you a
usable DVD, but this is nothing you may rely on. Growisofs cannot give
you more than cdrecord gives you with pipes.

BTW: because it is a well known problem to make backups from life filessystems, 
modern Operating Systems did develop filesystem snapshots. If you use snapshots,
there are no problems with _both_ growisofs _and_ cdrecord and this is the only 
_reliable_ way to use pipes with mkisofs on life filesystems.

If you do not run a modern OS and thus lack snapshots, I recommend you to 
upgrade to a modern OS that supports snapshots. Both Solaris and FreeBSD
support filesystem shapshots since ~ Y2000.

The only other reliable way to do streaming backups from filesystems is to use
the method from the time _before_ filesystem snapshots have been introduced: 

-	Bring you computer down to single user mode

-	Make the backup from a now stable filesystem

-	Bring the system back to multi-user mode

If you are on an older OS and cannot upgrade to a recent OS, this is the only 
way you may do backups.


 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js@cs.tu-berlin.de                (uni)  
       schilling@fokus.fraunhofer.de     (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/old/private/ ftp://ftp.berlios.de/pub/schily

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