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Re: HDD duplication in RH7.3



On Mon, Sep 02, 2002 at 10:11:24AM +0100, Stephen C. Tweedie wrote:
> On Mon, Sep 02, 2002 at 12:27:35AM +0800, karhong ng wrote:
>  
> > I have an internal HDD running under RH7.3. I would like to purchse a second HDD(usb external) of same geometry, and use it as a bootable snapshot of the first internal HDD.
> > 
> > I wish to make a whole disk bootable backup regularly via this method.
> > Is this feasible ?
> 
> If the disk is still mounted, then there are basically no guarantees
> if you try this.  You won't get a coherent snapshot of the disk.

  Hum, can we hazard in enhancement requests land ? Multics in the 70's
had that feature allowing to snapshot and backup coherent versions of
a filesystem while live. The evolution from ext2 to ext3 seems to make
this feature easier to implement since, if I understand correctly, when
a file is overwritten, the initial blocks of the file could be preserved.
Am I wrong ? Sounds to me that this feature would get ext3 closer to
what high availability systems really need.

> "Rsync" often works better --- it does a logical copy through the
> filesystem so it's entirely safe wrt. the VFS, and it is superb at
> doing incremental copies.

  I second that, I'm a really happy user of rsync and for localdisk to
localdisk, it's blazingly fast ! In most cases it's sufficient, except for
example if you don't have a /boot partition, you can garantee that the
information needed by the booloader will still be present at the beginning
of the disk (but for USB boot it probably doesn't matter.)

Daniel

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Daniel Veillard      | Red Hat Network http://redhat.com/products/network/
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