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RE: [Xen-users] Convert CentOS system to Xen image?

To: "Igor Chubin" <igor@xxxxxxx>
Subject: RE: [Xen-users] Convert CentOS system to Xen image?
From: "Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>
Date: Wed, 2 Apr 2008 10:28:11 -0400
Cc: James Pifer <jep@xxxxxxxxxxxxxxxx>, Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-users] Convert CentOS system to Xen image?
Igor Chubin wrote:
> ...
> > > You can use dd or cat (+ netcat | ssh)
> > > and it will copy raw image,
> > 
> > Yes, but that makes a lot of assumptions about the source and
> > destination systems that might not be true, like, the source
> > system is physical and the destination virtual, so the
> > destination will have different disk names, the source may
> > have software RAID1, but the destination being virtual may
> > already be backed by RAID1 and not need it. The source disk
> > may be infinitely bigger then the allocated destination
> > (ie source drive 250GB, root partition is 16GB LV and only
> > 3GB of it is used, but netcat'ing will try to transfer full
> > 250GB into a 16 or 32GB guest volume).
> I agree with you.
> My advice is related to particular (described earlier) task.
> ...
> > > Disatvantage:
> > >
> > > 1. You should create LVM and FS first.
> > >
> > 
> > I don't think I grasp your advantages/disadvantages points
> > here, maybe it's a language barrier where the subtleties
> > were lost in translation.
> My mother tongue is Russian and my English is very very poor.
> It's really hard to quickly express my thoughts in English.
> Excuse me Ross, and all who read this (and other my postings 
> to the list).
> When I say that dd/cat + netcat usage has advantage over 
> LVM+FS+rsync/scp/dump usage in the particular case, 
> I mean:
> when you use cat/dd you can copy system quick and dirty, 
> but when you use high level tools for copying files, 
> you should create volumes and filesystems before copying.
> I stress, that cat/dd one should use only
> in particular cases (for "quick-and-dirty" migration). 
> And for full featured migration
> it's better to use LVM/FS and other high-level tools.
> > I do agree that LVM is the way to go, as it's pros far
> > outweigh it's cons.
> >
> Ross, I think that I fully agree with you
> (except the fact that I think that there are many
> tasks where dd/cat is enough).
> > > >
> > > > For data partitions like /home you can do a dump, sftp, and restore.
> > >
> > > Also you can use rsync
> > > (it should be installed on both hosts).
> > 
> > rsync will indiscriminately copy-over files that it shouldn't.
> What do you mean?

Well rsync was really designed to replicate data from
one system to another, but this isn't technically
replication here as not all configs will be the same.

If it's a data volume like /home, then you might get
by with rsync. I have found though that the time to
get rsync going efficiently doesn't pay for a one
time operation. If this is done over a secure
reliable network and not the Internet, you could do
a dump | ssh restore type deal, maybe add a gzip
step in there to compress over the wire and it's

I have been playing around with the idea of using
something like 'revisor' from Fedora to capture
the basic system settings and packages into a
kickstart install iso that you can use to install
a PV that's identical to the source. Have it do
an RPM audit of all config files except a few
key ones like fstab, ifcfg etc and such and tar
those up and have it extracted in the %post
section of the kickstart... It's an interesting
idea... Hmmm


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