Disk cloning

[Dimitri Yioulos]

On Tue, 20 Jan 2009 12:35:05 +0100, Tino Schwarze wrote
> Hi,
> 
> On Tue, Jan 20, 2009 at 04:43:04PM +0530, Paniraja_KM at dell.com wrote:
> 
> > Cloning using dd is not a good option if the disk size is huge. This
> > will take lot of time for completion.
> > 
> > Its better to use 
> >  tar cvfz - * |ssh <user_name at server_name> tar xvfz \-
> >
> 
> He's talking about making a remote clone. I suppose, they've got one
> working system at a colo and want a second one there.
> 
> > -----Original Message-----
> > From: linux-poweredge-bounces at dell.com
> > [mailto:linux-poweredge-bounces at dell.com] On Behalf Of Dimitri Yioulos
> > Sent: Tuesday, January 20, 2009 4:28 PM
> > To: linux-poweredge-Lists
> > Subject: Disk cloning
> > 
> > Hello to all.
> > 
> > I hope it's OK to ask the following:
> > 
> > I've been asked by a company to remotely clone a working system. It's
> > colo'd in Virginia (company HQ is in New York, I'm in Massachusetts).
> > Physical access to the box, a PE 2950, I believe, is via "Remote Hands"
> > only - colo personnel can do minor things, including disk swaps.  Down
> > time is really not an option.
> 
> Down time is not an option - it's an requirement since you want your
> system in a consistent state.
> 
> > I've considered all of the various cloning tools, and it seems to me
> > that dd and rsync are best-suited to the task.  It looks like "dd
> > if=/dev/sda of=/dev/sdb bs=4096 conv=notrunc,noerror" will accomplish
> > the cloning (sda and sdb are of the same make, model, and size).
> 
> That will work.
> 
> > My questions:
> > 
> > 1.  Is the above dd command correct?
> 
> You might want to use dd_rescure instead if your worry about disk
> errors. (I'd worry about swapping disks ASAP if there was any error.)
> 
> > 2.  After cloning, must sdb be disconnected so as not to cause booting
> > problems?
> 
> No.
> 
> > 3.  Do I have to do anything post-cloning to make sdb bootable?
> 
> No. You get an exact image. Your sdb will work as a new sda in the new
> system (given that the system is exactly equal). You might want to mount
> your root and modify network addresses or similar (if not obtained via
> DHCP).
> 
> > 4.  What rsync command would I use to keep the two disks synced?
> 
> > If anyone has gone through this process, and can provide guidance, I'd
> > appreciate it.
> 
> Please explain with more details what you are trying to accomplish and
> what your setup is.
> Do you have two servers? (sda and sdb are in the same server, aren't
> they?)
> 
> If you want to keep some kind of hot-standby, an rsync command like this
> would do:
> 
> rsync -e ssh -a --exclude=/etc/sysconfig/network/* /home /srv /root /usr /etc 
> $standby-server:/
> 
> As I said: The question is what are you trying to accomplish?
> 
> Bye,
> 
> Tino.
> 

Tino,

sda and sdb reside on the same box.  The company has an old version of Ensim running on
this box, and needs to continue using it in the near-term.  However, it's no longer
available for Linux, and the company doesn't have the license key any more (the
company's bad, I know, but ...).  The company is concerned that if sda goes south
they'll be in deep stuff.  Hence, the need to clone sda.

I understand about disk consistency but, really, the system can't be brought down for
any length of time, and there's no one available at the colo to do tasks like inserting
CDs or DVDs.  so, most everything has to be done remotely on a live system.  The job
could be done during s0-called "quiet time", say 3:00AM.

Hope that's enough info to understand what I'm trying to accomplish.

Dimitri

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