[CentOS] EL6: Hard Disk upgrade howto?

Robert Heller heller at deepsoft.com
Sat Jul 30 15:18:34 UTC 2011

At Sat, 30 Jul 2011 09:12:28 -0500 CentOS mailing list <centos at centos.org> wrote:

> On 7/30/11 2:03 AM, Benjamin Smith wrote:
> > On Friday, July 29, 2011 08:02:20 PM Les Mikesell wrote:
> >
> >  > If the machines are pretty much identical, clonezilla should work. Boot
> >
> >  > the machine with a 'clonezilla-live' CD or USB drive. If you can attach
> >
> >  > the target drive to the same machine you can go disk->disk. Otherwise,
> >
> >  > connect to something on the network with enough space to hold the image
> >
> >  > (ssh, nfs, or a windows share) and clone disk->image, then boot the target
> >
> >  > machines and copy image->disk. There is also a server version that will
> >
> >  > pxe-boot the targets if you need to do a large number of them.
> >
> >
> > Thanks for the tip! I'll be trying this out on Monday, but what is the "native"
> > way of doing this?
> For disk image copies, you can use 'dd' with the raw disks.  But it won't know 
> anything about the filesystem and will copy all sectors.  Clonezilla will use 
> partclone (or ntfsclone for windows) and only copy the used blocks so it is much 
> faster with large disks.  In any case the partitions must be unmounted or at 
> least not changed while being copied, so you need to boot from something else. 

dump/restore is a 'native' file system copy method.  Doing this in
single-user mode works extremely well, although the really paranoid can
always boot up either a live cd or the boot/install cd in rescue mode.
I've done this countless times in either single-user mode and sometimes
in full multi-user mode (on a 'quiet' system).  (dump can dump
*unmounted* file systems.)

dd can be problematical if the target and source disks are different
(sizes, geometry, etc.), since dd will do a literal sector-by-sector
copy, which is not generally advisable (and why o why to people *keep*
suggesting it? -- it is really a misuse of dd, unless you *really* know
what you are doing).

> I recommend the ubuntu-based version of clonezilla for better hardware support. 
>   Also, you'll need to fix up the network settings and hostname on each clone 
> after you  bring it up.

Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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