Re: [Xen-users] Installing Xen on Debian Sarge

[Mark Foster <mark@xxxxxxxxx>]

Miguel Enrique Cobá Martínez wrote:

> 2. They are all about installing on plain devices, not lvm volumes.
If you are serious about using Xen for production systems you will want 
use LVM or something other than simple file-based disks. Sounds like 
some others are using true SANs or gnbd or drbd? My personal preference 
is to assign an 8GB logical volume for "/" and another volume for swap, 
the size depending on how much RAM will be assigned to the DomU. That 
fits my bill, but in the physical world I much prefer giving separate 
partitions for /boot, /usr, /var and so on. It's just too much 
(maintenance) overhead with virtual systems. I also prefer to use RAID 
0+1 over SCSI.
> I will be testing a distributed system I built for work. For this I need
> a central node and 10 remote nodes. I thought that Xen will be the
> perfect solution. Just create 11 DomUs with minimal debian in each one,
> run the test of the system and collect statistics.
>
> I have put a lot of time in my current desktop, so I would like to
> continue using my desktop, but running as Dom0. I would like to use the
> second hard drive to install the virtual machines.
I would recommend a dedicated system for Xen Dom0, as running it on your 
desktop is asking for trouble. Running your desktop in Xen as a DomU is 
also silly.
Keep your Dom0 as small as possible to minimize your risk when patching 
(you are patching right?)
> After a lot of problems and 3 days of search and testing I finally
> booted my machine as Dom0. These are the steps I followed:
>
> 1. I used the unstable pkgs for xen
OK.

> 2. I downloaded the src from:
> http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads/xen-2.0.7-src.tgz 
>
> and compiled using my current kernel config in /boot.
Huh? You used the pkgs AND you installed from src?

> 3. I installed the new XenLinux kernel in /boot and configured menu.lst
> according.
> 3. I had to build a initrd image so that the boot process could mount
> the root partition on lvm. I use the script from
> /usr/share/doc/lvm2/examples/lvm2create_initrd.gz
> to build the initrd, as mkinitrd has a bug with lvm root partitions.
Ah, good info!

> 4. I updated grub to use the initrd and all worked ok.
>
> After that, I had my system running Xen but without graphical setup.
> This is  not a problem, as I probably could configured correctly with
> patience.
> I am now ready for creating domains for the real work and I can say that
> I have managed to install Xen successfully.
> In spite of that, I have the feeling that the solution isn't optimal or
> the best.
>
> So, the questions:
>
> - I'm doing this the proper way? 
> - Is this the intended way of installing Xen?
> I mean, should I use my configured and personalised original machine
> (postgresql, apache, firefox, thunderbird, /home, etc) on top of Xen as
> Dom0 and from time to time to create DomUs for specific task? Or should
> I use a minimal debian for Dom0, just for hosting the DomUs and use one
> of the DomU as workstation, with all my configuration and selection of
> packages inside and the other DomUs for working as needed?
I wouldn't do what you are doing, but to each his own.

> - If I use Dom0 for my workstation, I think I will have full control of
> all the others DomUs, and I could use them as I wanted. I could access
> it with xm console without problems. But if I use one DomU for my
> workstation how could I access the other DomUs? With ssh or vnc only?
> What happend if I wanted to access the DomO from DomU? I think that I
> couldn't do that.
ssh or vnc or whatever! The only thing you lose is console access from 
your desktop to the DomUs, but that can be done by ssh-ing to DomO and 
'xm console' from there.
> - What will pass with the updates of my kernel in Dom0?  Will I need to
> redo all the steps for configuring my new xen-enabled kernel, creating
> an initrd image, compiling nvidia drivers and, when my Dom0 was updated,
> then update all of my DomUs?
You can specify a default kernel in /boot/grub/menu.lst you will 
sidestep any kernels installed via apt-get (or aptitude)
> A don't want to create a flame war, but I would like to hear the
> scenarios you used and the decisions you made when configuring Xen.
> Also, I would like to read your toughts about your use of Xen.
Using LVM was a good idea. LVM snapshots are also interesting way to 
save disk space and have multiple systems based on a common denominator, 
but I have yet to get that going. If anyone else has, I'd sure like to 
know how to set it up "right".
Good luck.

--
Some days it's just not worth chewing through the restraints...
Mark D. Foster, CISSP <mark@xxxxxxxxx>  http://mark.foster.cc/



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