- Open Source Workshop #2 - Voyage Linux Introduction
- Spam protected email address for mailman archive
- Subversion to DVCS - Your mindset has to change as well
- DNMA92, ath9k and hostapd with Voyage Linux
- Slides for Open Source Developer talk at SFD
- Open Source Developer talk at Software Freedom Day 2009 HK
- Building compat-wireless drivers for 2.6.30
- leds-alix2 module in 2.6.30 kernel
- squashfs 4.0 on Debian Lenny and 2.6.30 kernel
- Upgrade Debian Etch Xen 3.0.2 to Lenny Xen 3.2
Virtualization in Debian Etch (Part 3 - Xen)
In Part 1 and Part 2, we have explored running virtual machines using UML and KVM and benchmarked their performance comparing to the real machine. In Part 3, we will investigate Xen. If you are not familiar with Xen, here is the description from KernelNewbies
Xen is a hypervisor based virtualization technology originating at the University of Cambridge nowadays developed largely by the company XenSource. Xen introduced the concept of paravirtualization, which allows for extremely high performance virtualization provided that the guest virtual machine runs a modified operating system kernel. ...
Follow this step-by-step instructions, you will be able to:
- install Xen hypervisor and related tools from the Etch repository, without building from source files or compilation of kernel
- create virtual guest image and install Debian Etch on it
- start, run and manage Xen virtual guest systems
- compare the performance of difference virtualization technologies - UML, KVM and Xen
1. Installing Xen kernel, hypervisor and related toolsTo install the required software, run:
# apt-get install xen-linux-system-2.6.18-4-xen-686 xen-tools \ xen-docs-3.0 libc6-xen xen-hypervisor-3.0.3-1-i386-pae \ xen-linux-system-2.6.18-4-xen-vserver-686 bridge-utils
This will install the patched Xen kernel, the hypervisor, and all other tools that need to manage virtual machines and create virtual machine images. The heart of Xen is the hypervisor, which gets booted by the customized boot loader and controls cpu and memory, sharing them between the administrative domain (Domain 0) and the virtual guest systems.
It is now the right time to reboot. After restart, the system should display that you are running a kernel ready for Xen. That also means you are running Domain 0 (dom0):
Linux punknix-xen 2.6.18-4-xen-686 #1 SMP Thu May 10 03:24:35 UTC 2007 i686 GNU/Linux
A domain management service, Xen Daemon (Xend), performs system management functions related to virtual machines. It forms a central point of control for Domain 0 and can be controlled using an HTTP-based protocol. It must be running in order to start and manage virtual machines.
The first step for configuring xend is to setup bridge network for the guests. Edit /etc/xen/xend-config.sxp:
(network-script network-bridge) #(network-script network-dummy)Comment the original "(network-script network-dummy)" and enable "(network-script network-bridge)" line. Xend even allows you to define more comprehensive network setup, but network-bridge should be good enough for beginners.
Then restart Xen Daemon by:
# /etc/init.d/xend restart
2. Creating Debian Etch virtual guest system (domU)Before we create virtual guest image, edit /etc/xen-tools/xen-tools.conf to define the default values.
#lvm = punknix-xen dir = /home/xen debootstrap = 1 size = 4Gb memory = 128Mb swap = 256Mb fs = ext3 dist = etch image = sparse kernel = /boot/vmlinuz-2.6.18-4-xen-vserver-686 initrd = /boot/initrd.img-2.6.18-4-xen-vserver-686 mirror = http://ftp.hk.debian.org/debian/There are two options to store guest system in loop-back file image file or in LVM. In above xen-tools.conf, we will use the loop back image file (dir = /home/xen) to store the guest system. But you may want to consider LVM if you prefer a "standard" way in managing virtual server images. In this section, we will create guest system on a file image, but we will explore LVM in the later section:
Guest systems will be stored in /home/xen directory. Create it if it does not exist:
# mkdir /home/xenThen, create the guest system images with the following commands:
# xen-create-image --hostname=punknix-xen1 --size=4Gb --swap=256Mb \ --ip=192.168.1.93 --netmask=255.255.255.0 --gateway=192.168.1.1 \ --dir=/home/xen \ --debootstrap --dist=etch --mirror=http://ftp.hk.debian.org/debian/ --passwdxen-tools package provide handy and useful scripts to ease the creation of fully configured Xen guest domains (domU) which can be listed, updated, or copied easily. The above command is self-explanatory:
- creates the guest system with hostname punknix-xen1, with 4G root partition and 256MB swap
- assigns static IP 192.168.1.93, netmask 255.255.255.0 and 192.168.1.1 as default gateway.
- stores the guest system in /home/xen
- installs Debain Etch from ftp.hk.debian.org/debian through debootstrap and interactively asks for root password after installation
======================================================== General Information -------------------- Hostname : punknix-xen1 Distribution : etch Fileystem Type : ext3 Size Information ---------------- Image size : 4Gb Swap size : 256Mb Image type : sparse Memory size : 128Mb Kernel path : /boot/vmlinuz-2.6.18-4-xen-vserver-686 Initrd path : /boot/initrd.img-2.6.18-4-xen-vserver-686 Networking Information ---------------------- IP Address 1 : 192.168.1.93 Netmask : 255.255.255.0 Gateway : 192.168.1.1 Creating swap image: /home/xen/domains/punknix-xen1/swap.img Done Creating disk image: /home/xen/domains/punknix-xen1/disk.img Done Creating ext3 filesystem on /home/xen/domains/punknix-xen1/disk.img Done Installing your system with debootstrap mirror http://ftp.hk.debian.org/debian/ Done ... ========================================================After a coffee break, root filesystem images and swap image should be created under /home/xen
3. Starting Xen virtual serverxen-create-image script automatically generates domain configuration files to ease the setup work for users. The domain configuration file of our newly created domain will be saved in /etc/xen/punknix-xen1.cfg. Before starting virtual server, you may want to review or edit the domain configuration.
Another domain management tool, xm, is the primary tool for managing Xen from the console. Use "xm create" to start the virtual server just created:
# xm create /etc/xen/punknix-xen1.cfgOnce the virtual server is started, you can connect a virtual console with command:
# xm console punknix-xen1To verify how Xen manages the network interface, we run ifconfig on dom0:
vif1.0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link UP BROADCAST RUNNING NOARP MTU:1500 Metric:1 RX packets:6 errors:0 dropped:0 overruns:0 frame:0 TX packets:12 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:384 (384.0 b) TX bytes:4031 (3.9 KiB)Since we used bridge network, you can also see that Xen found a bridge interface and add the virtual interface to the bridge automatically:
# brctl show bridge name bridge id STP enabled interfaces br0 8000.0016013e2bd6 no eth1 eth2 vif1.0And you can ping to domU punknix-xen1:
# ping -c 2 192.168.1.93 PING 192.168.1.93 (192.168.1.93) 56(84) bytes of data. 64 bytes from 192.168.1.93: icmp_seq=1 ttl=64 time=0.096 ms 64 bytes from 192.168.1.93: icmp_seq=2 ttl=64 time=0.101 ms --- 192.168.1.93 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 999ms rtt min/avg/max/mdev = 0.096/0.098/0.101/0.010 ms
4. Create Xen with LVMThis section demonstrates the use of LVM for virtual images instead of loop-back image.
Before creating guest image, make sure you have free space in the volume group.
root@punknix-xen:~# vgs VG #PV #LV #SN Attr VSize VFree punknix-xen 1 8 0 wz--n- 233.52G 84.27GUse the same xen-create-image script to create the image but this time supplied with parameter --lvm=<volume group>.
# xen-create-image --hostname=punknix-xen2 --size=4Gb --swap=256Mb \ --ip=192.168.1.94 --netmask=255.255.255.0 --gateway=192.168.1.1 \ --lvm=punknix-xen \ --debootstrap --dist=etch --mirror=http://ftp.hk.debian.org/debian/ --passwdThe above creates Debian Etch virtual guest image using volume group punknix-xen. After another coffee break, two logical volumes were created:
# lvscan ... ACTIVE '/dev/punknix-xen/punknix-xen2-disk' [4.00 GB] inherit ACTIVE '/dev/punknix-xen/punknix-xen2-swap' [256.00 MB] inheritWe now have two Xen virtual guest systems ready!
5. PerformanceAgain, we benchmark different virtualization technologies by measuring Voyage Linux kernel build time. Do you believe in near native performance in Xen? Here is the result:
|Host OS||Athlon 64 X2 4400+|
Memory: 2GB Ram
|UML||Memory: 128MB (use tmpfs)|
Disk Image: 4GB
QEMU Disk Image: 4GB
|Xen - File Image||Memory: 128MB|
File Image: 4GB
|Xen - LVM||Memory: 128MB|
LVM Root: 4GB
It is a bit surprise to see that running guest system on file image is faster than on LVM in a small fraction. Also, the paravirtualization approach and HVM hardware help the virtualization performance a lot.
It is known that Xen also supports full virtualization that allows running unmodified operating systems such as Windows on processors with Intel VT or AMD-V technology. We will investigate full virtualization in Xen in the coming future. Meanwhile, you may refer to this thread for setup example.
Reference:The below lists additional references for writing up this article:
 - http://www.howtoforge.com/debian_etch_xen_from_debian_repository
 - http://wiki.kartbuilding.net/index.php/Debian_Etch_Xen_Install
 - http://www.cosmocode.de/en/blogs/gohr/20070130123639/index.html
 - http://etbe.blogspot.com/2007/01/installing-xen-domu-on-debian-etch.html