[CentOS] Transferring system to new drive

Robert Heller heller at deepsoft.com
Tue Sep 14 13:13:59 EDT 2010

At Tue, 14 Sep 2010 12:13:53 -0400 CentOS mailing list <centos at centos.org> wrote:

> On Tue, Sep 14, 2010 at 9:39 AM, Scott Robbins <scottro at nyc.rr.com> wrote:
> > On Tue, Sep 14, 2010 at 09:03:13AM -0400, Robert Heller wrote:
> >> At Tue, 14 Sep 2010 13:12:46 +0100 CentOS mailing list <centos at centos.org> wrote:
> >> >
> >> > Is there a document with instructions for this?
> >> > I've had smartd warnings that a hard disk in my server is sick,
> >> > so I am installing a new drive (in addition to the old).
> >>
> >> Here is an article I wrote about doing this:
> >>
> >> http://www.deepsoft.com/2009/01/how-to-transfer-a-linux-system-from-one-disk-to-another/
> >
> > As someone who came from FreeBSD, dump restore was always considered
> > best there.  Hoewver, I've heard (though not deeply investigated), that
> > due to various things in the Linux kernel, dump restore isn't the best
> > approach for Linux, and there will be metadata loss.  DISCLAIMER--this
> > isn't something I've really looked into, however last time I was going
> > to do it, I saw enoughw warnings about it to make me look for another
> > method.  If Robert has been doing it successfully, then, chances are
> > he's right.  (Perhaps these changes in the Linux kernel are newer than
> > the CentOS kernel.)
> FWIW, I only use dump/restore on unmounted or mounted read-only filesystems
> There was the email below (old, I know, but probably the source of the
> "dump restore isn't the best approach for Linux" thought):

I *suspect* that whatever was going on (metadata corruption) has long
since been fixed.  I've *never* had any problems with using dump and
restore, *even on live Read/Write filesystems while in full multiuser
mode*.  Generally, I don't do backups of *busy* file systems.  Given the
number of times I've done this, either the conditions that cause the
problems are exceedingly rare or else it is/was only really an issue with
bleeding edge kernels (I only ever used RedHat's not partitularly
bleeding edge kernels -- eg stock kernels from RH's distros).

> From: Linus Torvalds
> To: Neil Conway
> Subject: Re: [PATCH] SMP race in ext2 - metadata corruption.
> Date: Fri, 27 Apr 2001 09:59:46 -0700 (PDT)
> Cc: Kernel Mailing List <linux-kernel At vger Dot kernel Dot org>
> [ linux-kernel added back as a cc ]
> On Fri, 27 Apr 2001, Neil Conway wrote:
> > I'm surprised that dump is deprecated (by you at least ;-)).  What to
> > use instead for backups on machines that can't umount disks regularly?
> 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 roulette 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".
> Dump was a stupid program in the first place. Leave it behind.
> > I've always thought "tar" was a bit undesirable (updates atimes or
> > ctimes for example).
> Right now, the cpio/tar/xxx solutions are definitely the best ones, and
> will work on multiple filesystems (another limitation of "dump"). Whatever
> problems they have, they are still better than the _guaranteed_(*)  data
> corruptions of "dump".
> However, it may be that in the long run it would be advantageous to have a
> "filesystem maintenance interface" for doing things like backups and
> defragmentation..
> Linus
> (*) Dump may work fine for you a thousand times. But it _will_ fail under
> the right circumstances. And there is nothing you can do about it.
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Robert Heller             -- 978-544-6933
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