Xen 4.0.1 on Debian Squeeze dom0 and domU

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Most of the details on this page are from Debians much improved wiki page at http://wiki.debian.org/Xen


Installation of Xen on Debian Squeeze

aptitude -P install xen-linux-system
//At this point I prematurely rebooted and went
//xm list
//WARNING!  Can't find hypervisor information in sysfs!
//Error: Unable to connect to xend: No such file or directory. Is xend running?
//don't reboot. Follow the below:

mv /etc/grub.d/10_linux /etc/grub.d/21_linux

Additional Tweaks to make dom0 more stable

Limit RAM available to dom0

vi /etc/default/grub
#add the following
# Disable OS prober to prevent virtual machines on logical volumes from appearing in the boot menu.
#limit dom0 to 512MB RAM


Disable auto save and restore of domUs on host reboot

Apparently in Debians wiki, they say that saving the state of domU's on powerdown doesn't always work. Hence, disable the xen save and restore.

vi /etc/default/xendomains

Bridge Networking and disabling Memory Ballooning

vi /etc/xen/xend-config.sxp
#(vif-script vif-bridge)
(network-script 'network-bridge antispoof=yes')
#(enable-dom0-ballooning yes)
(enable-dom0-ballooning no)

Reboot dom0 and bring up Xen

xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0 15630    12     r-----     10.2

Create Virtual Machines - domUs

At this stage I used to manually setup lvm volumes and manually debootstrap the VM. See Create_DomU#LVM_Based_Setup_of_Virtual_Disk and Basic_Setup_of_Xen3.2_32bit#Create_DomU I'd then copy across resolv.conf, fstab, sources.lst as well as /lib/modules/2.6... etc. However with Etch and Lenny there was additional hassle tweaking inittab and the config to get the xm console to work properly.

With Debian Squeeze, I followed Debians advise on their wiki and started using Xen-Tools. It automates a lot and makes things much easier.

Using Xen-Tools to create VMs

apt-get install xen-tools
vi /etc/xen-tools/xen-tools.conf
#Below are all the uncommented lines I used:
lvm = vg1
install-method = debootstrap
size   = 20Gb
memory = 512Mb
swap   = 1Gb
fs     = ext3
dist   = `xt-guess-suite-and-mirror --suite`
image  = sparse
gateway    =
netmask    =
passwd = 1
kernel = /boot/vmlinuz-`uname -r`
initrd = /boot/initrd.img-`uname -r`
arch = amd64
mirror = `xt-guess-suite-and-mirror --mirror`
ext3_options     = noatime,nodiratime,errors=remount-ro
ext2_options     = noatime,nodiratime,errors=remount-ro
xfs_options      = defaults
reiserfs_options = defaults
btrfs_options    = defaults
nohosts = 1
pygrub = 1

Set Xen-Tools to use noop Scheduler

On the setup here with LVM volumes on top of RAID 1, it is more efficient and better for performance to have VM's use the "noop" I/O scheduler. I've asked people for feedback on this in #Xen on irc.freenode. See chat log below. Also, the following links give reference to this fact also. http://old-list-archives.xen.org/archives/html/xen-users/2010-04/msg00518.html http://prefetch.net/blog/index.php/2009/04/23/best-io-scheduler-to-use-with-virtualized-linux-hosts/

15:01 <@pasik> steviewdr: yes, you need to change the scheduler
15:01 <@pasik> steviewdr: new enough linux domU kernels automatically use
15:01 <@pasik> steviewdr: noop for virtual disks
15:03 < steviewdr> pasik: kernels newer than -> 2.6.32-5-xen-686? So its safe to use noop on domU's on lvm volumes?
15:03 <@pasik> steviewdr: yes, noop is safe and recommended
15:03 <@pasik> steviewdr: in domUs

You can check the current scheduler by going:

cat /sys/block/xvda2/queue/scheduler

You can set the scheduler by going:

echo "noop" > /sys/block/xvda2/queue/scheduler

We can set this noop scheduler option in the Xen-Tools template so all new VMs created get this noop scheduler.

vi /etc/xen-tools/xm.tmpl
#Add in the following:

Note: this line can also be added into a xen vm config in /etc/xen/vm01.cfg

Create VM

xen-create-image --hostname walle-vm01 --ip --vcpus 2

Set VM to autostart

mkdir /etc/xen/auto
ln -s /etc/xen/vm01.cfg /etc/xen/auto/

Start VM

xm create -c /etc/xen/vm01.cfg

http://old-list-archives.xen.org/archives/html/xen-users/2010-04/msg00518.html http://prefetch.net/blog/index.php/2009/04/23/best-io-scheduler-to-use-with-virtualized-linux-hosts/

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