Re: [Xen-devel] Automation scripts

[Brian Wolfe <ahzz@xxxxxxxxxxx>]

The best solution so far that I have found is to have 1 (or more) NFS
servers on a backside network that provide disk IO to the individual
XenLinux unprivileged domains. This allows me to restart a xenlinux
instance on a different machine should the primary fail. This also
allows me to have a more centralized filesystem that uses nfs/iSCSI on
LVM on raid-5 for reliability.

I'm far from having a working automated system right now. I still have
the iSCSI death issues to deal with when combining 2 iSCSI target
devices into a raid-1 array in Domain-0 to be exported to the XenLinux
unprived domain. 8-( NFS roots still periodically "lock up" momentarilly
(~2 to 10 seconds) when using nfs root. SO the solution isn't ready yet.
I do highly reccomend that people use LVM LVs for individual exportable
block devices and to forget about using COWs to "save space". Adding a
200GB disk is dirt cheap (unless you are talking about scsi) so it's not
worth the savings IMHO to multi-cow a filesystem into 2+ unprived
domains on a single machine. The 1 to 2 GB of saved space just isn't
worth it at $0.10 per GB of disk space. :) Add in the system overhead
and seek times required for COWs after your first FS upgrade and your
return is worse than using separate partitions/LVs in my experience. 

It's better  performance and maintainability wise IMHO to use a common
RO partition for your basic OS root fs and /usr and use the traditional
/etc, /var, /usr/local redirection to a tiny config partition and unique
/home partition for per-vhost files. This is only worth it IF you can't
afford the ~2GB for independant root and /usr filesystems.


For anyone using Debian Sarge for your Domain-0 (and unprived domains) I
have a repo that's updated when I see a "stable" snapshot go by. It can
be found at http://www.terrabox.com/debian. It's a simple debian
repository of binary and source. I'm still working on getting the
packaging refined and approved by my new-DM sponsor so that the
snapshots will make it into debian testing distro in the next month or
two.

I'm working on a first draft of a Debian on xen and LVM  howto. But like
Ian and group, dev work comes first till it doesn't flake out on me. ;)

If anyone is interested in a working HA solution using Xen for their
business, I can asist with design and deployment for a small donation to
my living expences fund. ;)

Brian Wolfe
TerraBox.com Inc.
linux and HA Contracting.

On Mon, 2004-09-27 at 16:53, Mark A. Williamson wrote:
> > Actually, I'd also be interested in any docs or information relating to LVM
> > with COW as an alternative to loopback images. If I want to be able to
> > shift my VM images about, can I do it with LVM? 
> 
> Shift them about between machines?  The ideal thing to do for that would be 
> to 
> keep a copy of the base image on all machines and just copy the changes to 
> that around your cluster when migrating.  I don't know how easy this is with 
> LVM...  Anyone?
> 
> > The section on this in the 
> > manual (5.2) is a little sparse on this subject to say the least! Guess
> > you're all too busy coding :o)
> 
> Yeah :-)  This manual might get a bit fleshed out before the 2.0 release but 
> I 
> was rather hoping someone who uses LVM would help out with the LVM 
> section ;-)  I just use dedicated partitions for domains.
> 
> Cheers,
> Mark
> 
> >
> > Cheers,
> > Paul
> >
> > On Tuesday 28 September 2004 07:23 am, Paul Dorman wrote:
> > > Hi all,
> > >
> > > I wonder if anyone on the list has written any scripts to automate the
> > > management of VMs with loopback images. Here's what I want to be able to
> > > do:
> > >
> > > * Store existing physical machine file systems, or pristine installs in
> > > loopback images on my Xen servers (something I'll do manually)
> > >
> > > * Run a script that will start a VM from one of these images,
> > > automatically associate it with a loopback device, give it a name, RAM
> > > allocation, network addresses, and set various internal parameters, such
> > > as hostname, routes, etc., based on a set of arguments. So something like
> > > "script <imagename> <hostname> <netconfigs> <RAM> <.. etc.
> > >
> > > * Have the same script take another argument that will cause it to clone
> > > a filesystem image first before starting the VM, so that I can use a set
> > > of images as VM templates. I intend to have a large collection of
> > > templates which my developers can use to create VMs suited to whatever
> > > project they are working on.
> > >
> > > * After a VM machine has been instantiated, I would like to be able to
> > > start and stop it with simple "start hostname" and "stop hostname" kinds
> > > of commands.
> > >
> > > * Have management tools so that I can for example shift a VM from one Xen
> > > server to another (shift hostname xenservername). These would also be
> > > used by load balancing scripts to shift machines around to manage
> > > resources.
> > >
> > > I'd like to build a web-based management system for these scripts, so
> > > that developers are free to create and control Xen VMs (though naturally
> > > with limitations based on what the servers can handle -- so my bosses
> > > will know when they need to buy me more servers :o)  ).
> > >
> > > I don't see these as particularly difficult, but if someone has done them
> > > already .... Also, I'd appreciate any thoughts you might have on
> > > automation of this kind, particularly in terms of functionality and
> > > practicalities.
> > >
> > > Thanks for your time!
> > >
> > > Paul
> >
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