Re: Looking for a backup to CD-R(W) program
On Tue, Nov 26, 2002 at 02:13:18PM -0500, Joe Nahmias wrote:
>
> 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".
May you should lvm a chance :) with lvm you can: 1) temporaly shutdown
services that could change filesystem, eg mysql, after that create a snapshot
of the filesystem. 3) start your services again 4) make backup of the
snapshot. Read lvm-howto for further information. I personally haven't
tried this, but it should work.
>
>
> > 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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--
Best regards,
Alexey Chetroi
---
Smile... Tomorrow will be worse. (c) Murphy's law
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