Virtual Machines working group
Members and assignment
Sander Klous - Nikhef (Chair)
Ronald Starink - Nikhef
Marc van Driel - NBIC
Pieter van Beek - SARA
Ron Trompert - SARA
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.
- Network Address Translation - What is the load?
- Virtual Machine Isolation - Prohibit internal network connectivity with IPTables.
- Image repository - Storage Area Network or distributed over worker nodes.
- Policy document
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
- 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
- A few additional staps were needed:
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
- 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
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/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
Network traffic for Virtual Machine management can be optimized significantly with two caches on each worker node:
- A read cache for the original Virtual Machine image to facilitate reuse on the same worker node.
- 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
- CERN June 2009 workshop on virtual machines