Re: Looking for a backup to CD-R(W) program
Chris,
I found the mail I alluded to before. It is also from linux-kernel...
You can see it at: http://old.lwn.net/2001/0503/a/lt-dump.php3
He seems to say that you can get a corrupted backup regardless of
whether you use CD-R(W) or not.
An excerpt:
====
Note that dump simply won't work reliably at all even in 2.4.x: the buffer
cache and the page cache (where all the actual data is) are not
coherent. This is only going to get even worse in 2.5.x, when the
directories are moved into the page cache as well.
So anybody who depends on "dump" getting backups right is already playing
russian rulette with their backups. It's not at all guaranteed to get the
right results - you may end up having stale data in the buffer cache that
ends up being "backed up".
====
Joe
> Gerald Livingston wrote:
> > On Mon, 25 Nov 2002 20:08:53 -0500 (EST) joe@nahmias.net (Joe
> > Nahmias) wrote:
> >
> >
> >> Chris,
> >>
> >> Correct me if I'm wrong, but I thought Linus himself said that
> >> using dump on live (mounted) filesystems was a bad idea. I'll see
> >> if I can dig up a reference to it...
>
>
> I did a quick search:
> http://search.alphanet.ch/cgi-bin/search.cgi?max_results=10&type=long&msgid=20011010173449.Q10443%40turbolinux.com&domain=ml-linux-kernel
>
> and found this email in the Linux kernel mailing list archive:
>
> > Andreas Dilger <adilger@turbolabs.com> wrote:
> >>
> >> Yes, but the only issue is if the filesystem is busy, you may get a
> >> bad backup for those files that have changed, but not for any
> >> files that have not changed during the backup.
> >>
> >> Reasons for not using tar or cpio include atime change and the fact
> >> that an "incremental" tar can't record the deletion of a file
> >> (AFAIK).
> >>
>
> I have not had any problems, but I am backing-up a home standalone PC
> and I do not multitask during the backup, so no files change during the
> backup. It would seem safest to boot into a second copy of Debian and
> run 'dump' from there. I do this for the large system backup anyway.
>
> Perhaps the 'changed file' problem is only an issue with 'cdbackup'?
> Presumably it would be accessing files during the backup process. In any
> case, backing up directly to CD seems to pose a much greater risk of
> backup corruption.
>
> Cheers,
>
> Chris.
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