Virtual Machines working group

Members and assignment

Sander Klous - Nikhef (Chair)<br\> Ronald Starink - Nikhef<br\> Marc van Driel - NBIC<br\> Pieter van Beek - SARA<br\> Ron Trompert - SARA<br\> <br\> Charge

Meetings

Kick-off - Monday July 6, 2009: agenda (dutch), minutes (dutch)

Presentations

Sky computing - Sander@nikhef.nl Klous (Monday July 6, 2009), a summary of the CERN virtual machines workshop (see other information) and an introduction for the kick-off meeting of the BIG grid virtual machines working group.

Open Issues

• Network Address Translation - What is the load?<br\>
• Virtual Machine Isolation - Prohibit internal network connectivity with IPTables.<br\>
• Image repository - Storage Area Network or distributed over worker nodes.<br\>
• Policy document<br\>

Infrastructure

We are setting up a testbed to investigate technical issues related to virtual machine management.

Hardware and Operating Systems

• Two Dell 1950 machines, dual CPU, 4 cores per CPU
  • One machine has a CentOS-5 installation
  • One machine has a Debian-squeeze installation

Software

• CentOS-5 comes with Xen 3.0
• Debian-squeeze comes with Xen 3.3
  • Debian-squeeze Xen packages have a problem with tap:aio.

Fix:
ln -s /usr/lib/xen-3.2-1/bin/tapdisk /usr/sbin
echo xenblktap >> /etc/modules

• Opennebula has been installed (stand alone) on CentOS-5 following this guide
  • A few additional staps were needed:
    • Install rubygems and rubygem-sqlite3
    • Opennebula has to be added to the sudoers file for xm and xentop
    • Sudoers should not require a tty

wget ftp://fr.rpmfind.net/linux/EPEL/5/x86_64/rubygem-sqlite3-ruby-1.2.4-1.el5.x86_64.rpm
wget ftp://fr.rpmfind.net/linux/EPEL/5/x86_64/rubygems-1.3.1-1.el5.noarch.rpm
sudo rpm -Uvh rubygems-1.3.1-1.el5.noarch.rpm rubygem-sqlite3-ruby-1.2.4-1.el5.x86_64.rpm 

In /etc/sudoers (on all machines)
opennebula ALL = NOPASSWD: /usr/sbin/xm
opennebula ALL = NOPASSWD: /usr/sbin/xentop
#Defaults    requiretty

• Installed iSCSI target and client software for shared image repository
  • Howtos: Debian client/server, CentOS client, CentOS server
  • Maybe test later with encrypted iSCSI
  • Two new machines ordered with the required iSCSI offload
• Image repository consists of LVM volume groups
  • Performance of LVM is better than file based images
  • Each logical volume contains an image
  • This allows easy creation/deletion of new images
  • VMs can run from cloned (Copy-On-Write) images

Implementation issues

Implemented iSCSI image management for opennebula following the storage guide

• Changed oned configuration as shown below
• Added tm_iscsi configuration
• Implemented transfer manager commands
• Modified XenDriver.cc and TransferManager.cc to support LVM images

In /opt/opennebula/etc/oned.conf:
TM_MAD = [
   name       = "tm_iscsi",
   executable = "one_tm",
   arguments  = "tm_iscsi/tm_iscsi.conf",
   default    = "tm_iscsi/tm_iscsi.conf" ]

/opt/opennebula/etc/tm_iscsi/tm_iscsi.conf
/opt/opennebula/etc/tm_iscsi/tm_iscsirc

/opt/opennebula/lib/tm_commands/iscsi/tm_clone.sh
/opt/opennebula/lib/tm_commands/iscsi/tm_delete.sh
/opt/opennebula/lib/tm_commands/iscsi/tm_ln.sh
/opt/opennebula/lib/tm_commands/iscsi/tm_mkimage.sh
/opt/opennebula/lib/tm_commands/iscsi/tm_mkswap.sh
/opt/opennebula/lib/tm_commands/iscsi/tm_mv.sh

.../one-1.2.0/src/vmm/XenDriver.cc
.../one-1.2.0/src/tm/TransferManager.cc

Local caching

Network traffic for Virtual Machine management can be optimized significantly with two caches on each worker node:

1. A read cache for the original Virtual Machine image to facilitate reuse on the same worker node.
2. A write-back cache for the copy-on-write clone to allow local writes when the virtual machine is active.

If requested by the user, the copy-on-write clone can be synchronized with the image repository when the virtual machine is done. After this synchronization, the write-back cache becomes obsolete and can be removed. We implemented both the read and the write-back cache at block device level (i.e. iSCSI/LVM level) with dm-cache. One LVM partition on the worker node serves as persistent local read cache for the virtual machine image. Another LVM partition on the worker node serves as transient local write-back cache for the copy-on-write clone. The transient cache is created and removed on demand by OpenNebula.

Unfortunately no CentOS or debian packages are available for dm-cache. Here is the recipe to build the kernel module from source.

On debian:
apt-get install linux-source linux-patch-debian
cd /usr/src
tar jxf linux-source-2.6.26.tar.bz2
/usr/src/kernel-patches/all/2.6.26/apply/debian -a x86_64 -f xen
cd linux-source-2.6.26
cp /boot/config-2.6.26-2-xen-amd64 .config
<In the Makefile: EXTRAVERSION = -2-xen-amd64>
make prepare
cp /usr/src/linux-headers-2.6.26-2-xen-amd64/Module.symvers .
cp -r /usr/src/linux-kbuild-2.6.26/scripts/* scripts
cd
wget http://github.com/mingzhao/dm-cache/tarball/master
tar zxvf dm-cache.tar.gz
cd dm-cache/2.6.29
ln -s /usr/src/linux-source-2.6.26/drivers/md/dm.h .
ln -s /usr/src/linux-source-2.6.26/drivers/md/dm-bio-list.h .
<In dm-cache.c: change BIO_RW_SYNCIO to BIO_RW_SYNC (line 172)>
<Create Makefile>
make
insmod dm-cache.ko
cp dm-cache.ko /lib/modules/2.6.26-2-xen-amd64/kernel/drivers/md/dm-cache.ko

Other information

• CERN June 2009 workshop on virtual machines