Comparison of Open Source Virtualization Technology

Fernando Laudares Camargos Gabriel Girard Benoit des Ligneris, Ph. D. [email_address] Comparative study of Open Source virtualization & contextualization technologies

Context (1)
Introduction
Why virtualize the server infrastructure
Virtualization technologies
The experiments
Explanations & anomalies
Which technology is best for ... you ?

Context (2)
Research executed by Fernando L. Camargos in pursuit of his Masters degree in Computer Science under the direction of Gabriel Girard (Université de Sherbrooke) and Benoît des Ligneris (Révolution Linux)
This being a research work, some questions remain unsolved... maybe you can help !

Why virtualize the server infrastructure (1) ? Server consolidation is the most mentionned argument

Why virtualize the server infrastructure (2) ?
Reduction of the purchase and maintenance costs
Compatibility with legacy applications and OSs
Security : environment to execute untrusty applications
Low cost environment for software development
Centralized control/management
Easy backup/restore procedures
Live migration
Quick server fail-over
High availability
Virtual appliances
Controled sharing of ressources
Cloud computing
Hardware abstraction
It's ... cool !

Full virtualization
Para-virtualization
OS-level virtualization ( contextualization )
Hardware emulation
Binary translation
Classic virtualization
Virtualization technologies (1)

Full virtualization
Para-virtualization
OS-level virtualization
( contextualization/
containers )
Hardware emulation
binary translation
Classic virtualization
Xen Linux-VServer OpenVZ KVM VirtualBox KQEMU Virtualization technologies (2)

virtualization != emulation
QEMU is an emulator Virtualization technologies (3)

Virtualization technologies (4) Virtualization technologies partial emulation no emulation KQEMU KVM VirtualBox OpenVZ Xen (Linux) Linux-VServer

2 types of hypervisors:
Hypervisors type I: KVM, Xen
Hypervisors type II: VirtualBox, KQEMU
Virtualization technologies (5)

The experiments (1) virtualization layer overhead But of how much ? To discover, we need to mesure the efficiency of the virtualization technologies efficiency = performance + scalability where :

Performance (overhead) : one virtual machine only
Scalability: several virtual machines
2 types of experiments: The experiments (2)

Virtualization solutions evaluated in this study
Chosen OSs:
Host: Ubuntu 7.10
VMs: Ubuntu 6.06
Test bed:
Intel Core 2 Duo 6300, 1.86GHz (x86_64 / VT-x)
4G Memory
Hard drive SATA 80G
The experiments (3)

64 bit kernel for all technologies
Use of VT extension for KVM, Xen
32 bit VM for VirtualBox
Identical memory allocation per VM for every technology but Vserver : 2039 Mo
Bits & Bytes & VMs : The experiment (4)

7 benchmarks (different workloads)
Reference : executed in the Linux host (scale = 1)
executed inside the virtual machines
4 execution sets
results = the average of the 3 last sets normalized by
the result obtained by the Linux host
Methodology : The experiments – Performance (1)

An equilibrated workload – a little bit of everything without stressing one particular ressource too much
Metric: given time for the completion of the compilation
Compilation of the Linux kernel tar xvzf linux-XXX.tar.gz cd linux-XXX make defconfig # ("New config with default answer to all options") --- date +%s.%N && make && date +%s.%N ... make clean date +%s.%N && make && date +%s.%N ... 3x The experiments – Performance (2)

The experiments – Performance (3)

Software for file compression
Using option that yields maximal compression which considerably increases the me m ory utilisation per process
Metric: given time for the completion of the compression
Bzip2 cd /var/tmp cp /home/fernando/Iso/ubuntu-6.06.1-server-i386.iso . date +%s.%N && bzip2 -9 ubuntu-6.06.1-server-i386.iso && date +%s.%N rm ubuntu-6.06.1-server-i386.iso.bz2 ... 4x The experiments – Performance (4)

Derived from the Netbench benchmark
Emulates the load imposed in a file server by n Windows 95 clients
n(umber of clients)=100, t(ime)=300
Metric: throughput (Mb/sec)
Dbench /usr/local/bin/dbench -t 300 -D /var/tmp 100 # 4x The experiments – Performance (6)

* no results for VirtualBox The experiments – Performance (7)

Application for low level (bit by bit) data copy
Mesures the performance of the I/O system (hard drive access)
2 tests:
copy of a single big file
copy of 60G of /dev/zero to /dev/null
Metric : throughput
dd ... dd if=/opt/iso/ubuntu-6.06.1-server-i386.iso of=/var/tmp/out.iso ... dd if=/dev/zero of=/dev/null count=117187560 # 117187560 = 60G ... rm -fr /var/tmp/* # between execution sets ... The experiments – Performance (8)

* no results for KQEMU nor VirtualBox The experiments – Performance (9)

* no results for KQEMU nor VirtualBox The experiments – Performance (10)

A benchmark that can be used to measure several aspects of the network performance
TCP Stream test : measure the speed of the exchange of TCP packets through the network (10 sec.)
Metric: throughput (bits/sec)
Netperf netserver # in the server .. netperf -H <nom du serveur> # in the client, 4x The experiments – Performance (11)

Similar to Netperf's TCP Stream Test, measures the performance of file exchange through the network
2 tests:
ISO file: 1 big file (433M)
Linux kernel tree: several small files (294M)
Metric: time (sec.)
Rsync .. date +%s.%N && rsync -av <server>::kernel /var/tmp && date +%s.%N ... date +%s.%N && rsync -av <server>::iso /var/tmp && date +%s.%N ... rm -fr /var/tmp/* # between execution sets ... The experiments – Performance (13)

Measures the performance of a DB server
Workload centered in I/O operations in the file system
Metric: throughput (transactions/sec)
Sysbench sysbench --test=oltp --mysql-user=root --mysql-host=localhost --debug=off prepare # (1x) sysbench --test=oltp --mysql-user=root --mysql-host=localhost --debug=off run # (4x) O n- L ine T ransaction P rocessing OLTP test statistics: queries performed: read: 140000 write: 50000 other: 20000 total: 210000 transactions: 10000 ( 376.70 per sec. ) deadlocks: 0 (0.00 per sec.) read/write requests: 190000 (7157.28 per sec.) other operations: 20000 (753.40 per sec.) The experiments – Performance (16)

Conclusion :
Linux-VServer: excellent performance. Has presented minimal to no overhead when compared to Linux.
Xen: has shown a great performance in all but the Dbench benchmark (I/O bound benchmark).
KVM's performance was fairly good for a full virtualization solution but should be avoided to run applications that strongly rely on I/O.

Conclusion (cont) :
OpenVZ has shown a very variable performance (from weak to excellent). Certainly because of accounting for I/O and because of some network optimization for the Network related tests.
VirtualBox has presented a good performance for the file compression and network based benchmarks. Poor performance for all the other situations.
KQEMU has shown a poor performance for all benchmarks. It is clear that this virtualization solution does not make a good use of the available ressources and its application in production servers should be avoided.

1 benchmark ( Sysbench, kernel compilation) executed by n VMs concurrently
n = 1, 2, 4, 8, 16 et 32
4 execution sets:
results = average of the last tree execution sets
Memory allocation per VM :
Methodology: * 1536 Mb (KQEMU) The experiments – Scalability (1)

The experiments – Scalability (2)

Conclusion :
The efficiency of virtualization solutions is strongly related to the number of VMs executing concurrently (scalability)
Most of the time, one additional VM helps to get the maximum performance out of a given server (link with the number of CPU)
More decreases performance as a bottleneck is limiting performance (CPU/core number important !)
Linux-VServer has shown the best global performance for up to 5-7 VMs.
Xen has proved to be the best full virtualization based solution.
Conclusion - Scalability (1)

KVM has shown a reasonable performance for a full virtualization solution.
OpenVZ's performance was not what we would expect of a contextualization solution. Our hypothesis is that the accounting (beancounter) is the root cause of th overhead
VirtualBox has shown an impressive performance, the total throughput has more than doubled when the number of VMs has pass from 8 to 16. However, we were unaible to execute this experiment with 32 VirtualBox VMs executing concurrently.
KQEMU's performance was weak when compared to all other solutions, independently of the number of VMs in execution.
Conclusion – Scalability (2)

Which technology to use in each case ? A technological point of view ...
OpenVZ : pure network related applications, thanks to the optimizations done in the network layer. Not indicated for I/O applications.
Linux-VServer: all kinds of situations ( a priori ).
Xen can also be used in all kinds of situations but requires important modifications in the guest OS kernels OR the use of the VT virtualization instructions.
KVM and VirtualBox have proven to be good options for development environments.
KQEMU has shown weak performance. It is indicated for development only.

Results are very different for every benchmark/technology ,so benchmark the technology you plan to use with your own mission critical application BEFORE virtualizing your servers (ex: File Servers benchmark).
Only Xen is actually supported by the industry (RedHat, SuSE, Mandrake, IBM, etc.)
KVM is available in the standard Linux kernel : Yeah! But poor performance overall ;-(
Linux-VServer and OpenVZ: they both need a modified kernel that is not officially supported by the afore mentioned giants of the industry but . . .
Conclusion : Which technology to use in each case ?

Since last OLS, key players like IBM, Intel, and Google are working hard to include a container based technology in the Linux kernel
Lots of patches from OpenVZ gets integrated into the kernel recently and everyone expects that we will have Really Soon Now a contextualization in the linux kernel without the need for any kernel hacking
We strongly believe that the integration of a contextualization/container solution is the best way to go for Linux-on-Linux virtualization needs
It will offer VMWare a very strong and completely open-source competition
Future / contextualisation

http://www.cio.com	222
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http://iocg.ignou.ac.in	12
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http://ciopreview.cwcxo.com:82	3
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Comparison of Open Source Virtualization Technology

by Benoit des Ligneris on Aug 07, 2008

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