Using Xen with Lustre

With Xen virtualization, a thin software layer known as the Xen hypervisor is inserted between the server's hardware and the operating system. This provides an abstraction layer that allows each physical server to run one or more "virtual servers", effectively decoupling the operating system and its applications from the underlying physical server.

You can deploy virtualization using one of two options: full virtualization or paravirtualization.

Full virtualization provides a total abstraction of the underlying physical system and creates a new virtual system in which the guest operating systems can run. No modifications are needed in the guest OS or application (the guest OS or application is not aware of the virtualized environment and runs normally).

Paravirtualization requires user modification of the guest operating systems that run on the virtual machines (these guest operating systems are aware that they are running on a virtual machine). The result is near-native performance.

You can deploy both paravirtualization and full virtualization across your virtualization infrastructure.

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Installing the Xen host

Should there be some content under this heading?

Creating a Xen Guest

1. Use virt-install to provision the operating system as shown in the example below: (Is the text in red correct?)

virt-install --paravirt --name=$NAME --ram=$MEM --vcpus=$NCPUS --file=$IMAGE --file-size=$IMAGESIZE \
             --nographics \
             --noautoconsole \
             --location=nfs:10.8.0.175:/rhel5/cd \
             --extra-args="ks=nfs:10.8.0.175:/home/parinay/xen-cfg/rhel5.cfg"

Should these options be explained here or a pointer be provided to Xen documentation that describes these options?

2. * config image . Example file for RHEL5. OK to replace the red text with something like the following?
Create a config image for the Xen guest. The example below for RHEL5 shows a configuration image in the form of a kickstart file generated by the Anaconda installation program. The kickstart image can be accessed from the host using NFS or HTTP. Please correct as needed.

# Kickstart file automatically generated by anaconda.

install
nfs --server 10.8.0.175  --dir /rhel5/cd
key --skip
lang en_US.UTF-8
keyboard us
text
network --device eth0 --bootproto dhcp
#rootpw --iscrypted $1$QQO.JRIi$kRVI0ntI.EWCvF9DpdNNp/
rootpw --iscrypted $1$wJCInuZ4$C.J3yKu/.a2Ce6cfo1kpV.
# firewall --enabled --port=22:tcp
firewall --disabled
authconfig --enableshadow --enablemd5
selinux --permissive
timezone --utc America/Los_Angeles
bootloader --location=mbr --driveorder=xvda
# The following is the partition information you requested
# Note that any partitions you deleted are not expressed
# here so unless you clear all partitions first, this is
# not guaranteed to work
clearpart --linux --initlabel --drives=xvda
part /boot --fstype ext3 --size=100 --ondisk=xvda
part /     --fstype ext3 --size=0 --grow --ondisk=xvda
part swap   --size=1000
reboot

%packages --resolvedeps
@core
@base
@development-libs
@system-tools
@legacy-network-server
@legacy-software-development
@admin-tools
@development-tools
audit
kexec-tools
device-mapper-multipath
imake
-sysreport


%post
/usr/sbin/useradd -u 500 lustre
/usr/sbin/useradd -u 501 user1
/usr/sbin/useradd -u 60000 quota_usr
/usr/sbin/useradd -u 60001 quota_2usr
mkdir /data
echo 10.8.0.75:/rhel5/cd /data nfs defaults 0 0" >> /etc/fstab

3. Modify the .config file for use with Xen. The entries in the .config file related to Xen are shown below: Please make whatever changes are needed to correct the text in red.

CONFIG_X86_64_XEN=y
CONFIG_XEN_PCIDEV_FRONTEND=y
CONFIG_NETXEN_NIC=m
CONFIG_XEN=y
CONFIG_XEN_INTERFACE_VERSION=0x00030203
#
# XEN
#
CONFIG_XEN_PRIVILEGED_GUEST=y
# CONFIG_XEN_UNPRIVILEGED_GUEST is not set
CONFIG_XEN_PRIVCMD=y
CONFIG_XEN_XENBUS_DEV=y
CONFIG_XEN_BACKEND=y
CONFIG_XEN_BLKDEV_BACKEND=m
CONFIG_XEN_BLKDEV_TAP=m
CONFIG_XEN_NETDEV_BACKEND=m
# CONFIG_XEN_NETDEV_PIPELINED_TRANSMITTER is not set
CONFIG_XEN_NETDEV_LOOPBACK=m
CONFIG_XEN_PCIDEV_BACKEND=m
CONFIG_XEN_PCIDEV_BACKEND_VPCI=y
# CONFIG_XEN_PCIDEV_BACKEND_PASS is not set
# CONFIG_XEN_PCIDEV_BACKEND_SLOT is not set
# CONFIG_XEN_PCIDEV_BE_DEBUG is not set
# CONFIG_XEN_TPMDEV_BACKEND is not set
CONFIG_XEN_BLKDEV_FRONTEND=y
CONFIG_XEN_NETDEV_FRONTEND=y
CONFIG_XEN_FRAMEBUFFER=y
CONFIG_XEN_KEYBOARD=y
CONFIG_XEN_SCRUB_PAGES=y
# CONFIG_XEN_DISABLE_SERIAL is not set
CONFIG_XEN_SYSFS=y
CONFIG_XEN_COMPAT_030002_AND_LATER=y
# CONFIG_XEN_COMPAT_LATEST_ONLY is not set
CONFIG_XEN_COMPAT_030002=y
CONFIG_HAVE_ARCH_ALLOC_SKB=y
CONFIG_HAVE_ARCH_DEV_ALLOC_SKB=y
CONFIG_HAVE_IRQ_IGNORE_UNHANDLED=y
CONFIG_NO_IDLE_HZ=y
CONFIG_XEN_UTIL=y
CONFIG_XEN_BALLOON=y
CONFIG_XEN_DEVMEM=y
CONFIG_XEN_SKBUFF=y
CONFIG_XEN_REBOOT=y
CONFIG_XEN_SMPBOOT=y

4. To build a Lustre-patched Xen guest image Is this correct?, follow the procedure Building Lustre Code.

5.In the initrd file?image?, check that the xenblk module has been loaded.

Note: When you boot as the guest, if you have problems with the network, the xennet module? may not be loaded. Enter:

depmod -a
modprobe xnenet
Cross check with lsmod

Debugging/Troubleshooting

• Mounting Xen disk images
  • Handling Linux based virtual hosts w/o LVM

find out what loop devices are already in use:

 
losetup –a 
losetup /dev/loop1 /data/images/rhel5.img
fdisk -l /dev/loop1
kpartx -a /dev/loop1

As the image file uses the loop0 device, the device files that have been created will have the names /dev/mapper/loop0p1, /dev/mapper/loop0p2 and so on. You can now use these files to mount the file system that the root of the virtualized operating system (OS) is installed on.

Once you have made all of the necessary modifications to this file system, un-mount everything properly by entering the following commands:

umount /mnt 
kpartx -d /dev/loop1 
losetup -d /dev/loop1 

• Mounting Xen disk images
  • Handling logical volumes in Linux-based virtual hosts

losetup –a 
losetup /dev/loop1 /data/images/rhel5.img
fdisk -l /dev/loop1
kpartx -a /dev/loop1

You will need to make sure that the partition is known by the LVM subsystem as a physical device. Knowing that the partition is a type 8e is not enough; you need to tell the LVM subsystem that it is available as a physical device and that the LVM can use it. Use the following command to do this:

pvscan /dev/loop0p2 

Next, you will be told that an LVM volume group has been found within the physical device, but you have to initialize this volume group manually by using this command:

vgscan

To complete the reconfiguration of the LVM structure, you need to do the same for the logical volumes in the volume group which can be done with this command:

lvscan 

Although you now have access to the logical volumes again, you'll see that all of the logical volumes are inactive. You need to fix this before the logical volumes can be mounted. To do this, change the status of the volume group by using the vgchange command. This command will change the status of all volumes in the volume group vm1vg to active:

vgchange /dev/vm1vg 

The LVM logical volumes are now active and ready to be mounted. For example, if you want to mount the logical volume with the name /dev/lvm1vg/root, you would use the following command:

mount /dev/vm1vg/root /mnt 

At this point you have full access to all of the files in the logical volume. You now can make all of the changes that you need to make.

• Cloning the disk images
• Enabling the console logging for guests

In /etc/init.d/xend, change the following lines to yes

XENCONSOLED_LOG_HYPERVISOR=yes
XENCONSOLED_LOG_GUESTS=yes

References

• Xen Community Mailing Lists
• Xen-org
• Xen Virtualization Essentials This link doesn't appear to be live
• Mounting Xen guest images
• Virtualization Guide

Misc

• For Ubuntu lovers Ubuntu/Xen

Omitted "Current Status of Project".