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Re: DVD-R as backup medium: growisofs + udftools

Joerg Schilling wrote:
"Thomas Schmitt" <scdbackup@gmx.net> wrote:


Joerg Schilling:
It is _impossible_ to do correct backups without additional disk space.
Giuseppe Corbelli:
You say it is necessary to store star archives on a filesystem prior
to backup?
It is possible to write archives as sessions
directly to multi-session media: DVD-R, DVD+R,
As long as one knows the start addresses it
is easy to read the archives by help of dd.
This works for afio as well as for star.

Try for example:
  find . | \
  afio -oZ - | \
  cdrskin -v dev=/dev/sr0 -multi -

It seems that you missunderstand reliability.

find | archiver

is a grant for inconsistence.

You left off "if any of the files are being written." What you said is true for filesystems which are changing, not correct for filesystems with all static content. As long as the user understands the limitations of the method, it presents no reliability issues.

You understand the issues, and could have clarified the limitations.
Using tar is gradually better but still not OK.
Do you like software for a toy environment or real reliable solutions?

It makes no sense to discuss religuous aspects like you try to do.
Rather thing abount constraints:

-	Big backups and incrementals do not fit on a single DVD.
	If you really like to use DVDs as media, use star -nultivol

Or other tools like 'breakup' which can split a large list of backup tasks to subtasks of limited size.
-	Small backups that fit on a DVD easily fit on intermediate disk space.

Note that you first need to think about snapshots anyway and snapshots
need disk space.

Snapshots only capture what's on the filesystem, which does not provide consistent data in all cases. If an application modifies multiple files, or multiple records in a single file, such that it buffers data in the application, partial data may be written at any instant in time. The application must be stopped or be able to bring the data to a known valid state on demand to provide perfect reliability. Fortunately most users don't have applications they can't stop, or the applications can insure data consistency internally, so this is just another exception case.

I can't think of anything other than a clean shutdown and backup from live CD boot which would handle every possible case.

Note: I'm not disagreeing with you just making some clarifications of which you are aware but others may not be.

Bill Davidsen <davidsen@tmr.com>
 "Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark

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