Replicating a live server on a domU

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On Tue, Oct 27, 2009 at 7:25 PM, Alexandru Florescu <alex@...> wrote:
> Hi,
>
> Has anybody ever stumbled upon the need to replicate a live and in
> production server to a virtual machine?

There's no way to do it that I know of. Not live anyway.
There are p2v solutions though. Google is your friend.

--
Fajar

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>
> Hi,
>
> Has anybody ever stumbled upon the need to replicate a live and in
production
> server to a virtual machine?
>
> I'm trying to virtualize a bunch of servers but I can't figure out how
can I
> mirror the file system. I do not want to start from scratch with them.
>
> The whole idea is to transfer them to the virtual side as they
currently are.
>

I do this on a semi-regular basis as part of backup testing for clients
(eg to make sure that their backups are good). In theory you can just
clone the disk and possibly fiddle with the CriticalDeviceDatabase and
Services/xxx keys to ensure that the IDE driver can be used for booting.

James

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Novell recently acquired a company called PlateSpin that does exactly this - currently the "live" functionality only works for Windows operating systems, but they're promising a version that will do Linux, soon, as well.  Linux can be done in the current version, but you have to bring the Linux system down - you can't do it on the fly.

-Nick



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Alexandru Florescu wrote:

>Has anybody ever stumbled upon the need to replicate a live and in
>production server to a virtual machine?
>I'm trying to virtualize a bunch of servers but I can't figure out
>how can I mirror the file system. I do not want to start from
>scratch with them.
>The whole idea is to transfer them to the virtual side as they currently are.

Yes, I've done it several times - all Debian GNU/Linux systems of
various vintages.

If you are prepared to modify the system, then install a Xen-ified
kernel environment first - it makes things simpler. I just install a
-xen kernel and let that take care of things like modules etc, but I
dare say there are more efficient ways to do it if you aren't using
pygrub.

Create new device files/volumes/whatever on the Dom0, mount them on
Dom0 (eg you might have /mnt /mnt/var /mnt/home etc), and copy the
filesystem across. Personally I normally use Rsync for this - but
don't forget to use the "--numeric-ids" option to avoid ownerships
getting mangled.

Before you unmount the volumes, go in and change things like fstab
and network settings. Also, if you didn't do it earlier, chroot to
the mountpoint (/mnt in the above example) and install the Xen-ified
environment.

Unmount the volumes, setup the guest config file, boot guest (use -c
option to attqch to console) and see what's broken.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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Hello.
Nice one Simon, that's the exact thing that I've done so far.
I went to stacklet.com and grabbed a xen-ready image for centos 5.3,
unpacked it, mounted it and then
"rsync -e ssh -avz --exclude=/proc --exclude=/lost+found --exclude=/boot /
xenserver:/mnt/centosimg" from the live server.
It copied pretty much everything but it also errored some stuff.
Now I can boot the machine, I can login, pretty much everything looks ok,
but it doesn't load any modules, and lsmod is empty.

The config file includes the following:
kernel = "/boot/vmlinuz-2.6.18.8-xenU"
memory = 256
name = "centos.5-3.x86"
vif = [ '' ]
disk = ['file:/vserver/images/centos/centos.5-3.x86.img,sda1,w']
root = "/dev/sda1"
extra ="fastboot"

My rsyncd centos was 2.6.18-164.el5.
The xen-ready centos, on stacklet it says that it's 2.6.18.8, but when I
boot it up it says that it's 2.6.18-128.1.6.el5xen. Anyway, the error is:
FATAL: Could not open
'/lib/modules/2.6.18-128.1.6.el5xen/kernel/drivers/block/aoe/aoe.ko': No
such file or directory

A ls /lib/modules reveals that I only have 2.6.18.8.xenU in there.
so I just rename the original 2.6.18.8.xenU to 2.6.18-128.1.6.el5xen and do
another modprobe aoe and I get:
FATAL: Error inserting aoe
(/lib/modules/2.6.18-128.1.6.el5xen/kernel/drivers/block/aoe/aoe.ko):
Invalid module format

I also rename the original 2.6.18-164.el5 to 2.6.18-128.1.6.el5xen and get
the same Invalid module format.

How did you get around this problem?
Thanks.









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Alexandru Florescu wrote:
>I went to stacklet.com and grabbed a xen-ready image for centos 5.3,

Why ?
You've grabbed a Xen ready image, then the first thing you've done is
overwrite it with your live server config.

>unpacked it, mounted it and then
>"rsync -e ssh -avz --exclude=/proc --exclude=/lost+found --exclude=/boot /
>xenserver:/mnt/centosimg" from the live server.
>It copied pretty much everything but it also errored some stuff.
>Now I can boot the machine, I can login, pretty much everything looks ok,
>but it doesn't load any modules, and lsmod is empty.

You might not have any modules to match the kernel - note below the
mismatch between kernel versions.

You've got a mismatch between the kernel image you are booting from,
and what's in your image.


I'm no expert, but I'd suggest your method is far from ideal.
Essentially your system is now a hybrid made by overwriting parts of
the filesystem, while leaving other bits intact. I'd suggest you
would be better making an EXACT clone of your live server into a
blank volume, and then adding a Xen kernel.

When using rsync, you've missed off two important switches. Firstly,
you've missed -H (--hard-links) so you'll have copied any hard linked
files as separate files. Secondly, you've missed --numeric-ids which
is essential when copying between systems (unless you are 100%
certain they both have the same users and groups) - without it,
you'll find your file ownerships mangled.
Once you've done it a few times, you tend not to forget :-/

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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