Virtual Servers compared

Today if you are looking for server virtualization solutions then there are quite a few of them available in the market that let you do server/OS partitioning as well as consolidation. So we decided to check out some of the most popular ones. These include the VMware, MS Virtual Server and

Xen.

We took a look at four of them, tested them in our labs and compared their features and performance against each other. To test these products we used IBM xSeries 225 server having dual 2.4 GHz Xeon processors with 2GB RAM and an SCSI (10k RPM) hard drive. We connected the server and its clients on a Gigabit network.

To test the performance of the virtual systems, we created two virtual machines instances. One running Windows XP with one dedicated processor (2.4 GHz), 512 RAM and 10GB of HDD space and other running PCQLinux 2005 with exactly the same specs. Then we ran Business WinStone 2003 on the Window XP instance and on Linux we timed a Linux Build (aka kernel compilation) run. We also ran the same tests while maxing out the resources of the Host OS to check whether it affected the performance of the virtual instance. We also have taken in consideration the usability and manageability of the product and mention them in detail here.

VMware ESX Server 2



VMware ESX Server is aimed at the server partitioning and consolidation needs of enterprises. The solution efficiently 



allocates hardware resources such as processor, RAM, storage and NIC to the virtual machines and lets you to utilize each bit of your server performance level. The server comes as a single bootable Linux CD with all the pre-requisites and the actual software in place. So to install you just need a single barebones machine (without any OS installed). The CD carries an older version of RedHat Linux and the installation of that is a piece of cake. After the installation you get a terminal-based Linux box. But all the management can be done from a remote machine over a Web browser. 

VMware Virtual Center Management tool lets you manage all the VMware's servers from a single interface VMware GSX server also has a GUI that lets you configure  virtual machines on the server

Coming to features, the product has SAN support and can boot the ESX host server from the SAN directly. Plus it can also be used to create a replica or take a backup of a virtual machine. It also has VMware Virtual SMP support for multi-processor virtual machines. ESX has built-in support for NIC teaming and creating VLANs. On the resource allocation front, the software supports Intel HT processors and lets you allocate multiple processors for different virtual machines. For storage, you can host virtual disks on a SAN and you can even emulate SCSI or IDE drives interface as needed. The NIC of the physical server can be shared evenly among the virtual machines or you can allocate them in dedicated mode for a particular running virtual machine. 

To manage the ESX, it gives you a Web interface, which lets you do every thing, from configuring hardware to running the virtual machines remotely. If you want to have more features such as proactive management and rapid OS deployment, you can buy VMware's Virtual Center Management software. This software is a virtual infrastructure management tool that lets you manage all VMware's virtual servers from one place. It lets you do proactive tasks like sending alerts and resetting virtual machines, if it smells something fishy on them. To rapidly deploy OSs, you just need to create templates of a base deployment and then the same template can be used to deploy further virtual machines. It has an 'Instant Provisioning Deployment Wizard' that lets you do this in less than 10 minutes. You can even make a clone of a virtual

machine and can restore it later in case of failure. The software gives you migration capability and using this you can migrate

virtual machines between VMware's virtual servers in your infrastructure. 

Moving to security, VMware ESX Server authenticates all remote users who connect to a server using the Web interface or the remote console. Network traffic between the server and the client are secure when using

SSH. 

Finally on the performance front, VMWare ESX server gave a decent score of 25.7 on Business Winstone on the Windows XP VM. The kernel compilation ran on PCQLinux with same specs and it clocked at 10 minutes 47

secs. 

Overall this product gave us the best performance among all the products we looked at. But it was not able to overshoot the 



performance of Xen in the kernel compilation test. 

VMware GSX Server 3



This is a variant of the ESX server which installs on top of an existing Windows or Linux OS. It is basically aimed at enterprises looking for a virtualization solution that is easy to setup on an

existing infrastructure. Feature wise, VMware GSX is a scaled down version of the ESX server and supports lesser number of

resources. This software does not have SAN and virtual SMP support. Also missing is the support for creating VLANs and NIC teaming. Since this software is installed over an existing OS with its own services and applications, the performance is comparatively lesser than that of the

ESX.

Web interface showing the health of MS Virtual Server 2005. Plus from the same, you can manage the entire virtual server

Coming to the management part, you can configure the virtual machines remotely by through its Web interface or you can use the VMware virtual machine console. It also supports the Virtual Center Management tool discussed earlier. That means you can set up proactive alerts and can do rapid OS deployment on the GSX server as well. Like the ESX, its also has failsafe clustering support, but only within the particular host server. However the ESX allows both intra-host and cross-host VMs. On the security front, GSX authenticates users connecting to the server and the traffic between the host and clients are transferred over an SSH tunnel. 

Performance wise, GSX gave a marginal performance drop over VMware ESX and a drastic drop when compared with Xen. It gave the score of 19 in Business Winstone and the Linux Build test took around 12 minutes 15

secs. 

MS Virtual Server 2005 



MS Virtual Server 2005 is the virtual machine solution for Windows 2003 systems. Like other virtual servers, this also emulates and runs multiple OSs concurrently on a single physical server. The solution is aimed at organizations that are looking for efficiency in software testing, development and server consolidation scenarios.

The product features a robust storage, networking capability and provides an easy to use Web interface. Its storage (virtual disk) is a file hosted on any medium the host server can use. Secondly, to boot the virtual machine from an ISO image over a network, you have to first copy the ISO to the host machine-however, this looks like a bug in this version. We did not see this problem with either VMware product. 

On the management front, the software allows you to manage and configure the virtual machine remotely with on your Web browser. You can even see and work on the virtual machine in the Web browser itself, seamlessly. Plus the same interface allows you to monitor the health of the virtual server. If you have multiple

deployments of MS Virtual Server 2005 on your network, you can use a single Web interface to manage all of them. This is a good feature that we did not see in the other offerings. However, the same feature can be realized in ESX/GSX using the VMware Virtual Center Management software. In addition, you can set up proactive alerts using MOM (Microsoft Operation Manager) and with the Virtual Server Management Pack. Still, compared with against VMware Virtual Center, we found MSVS 2005 lacking in features and detailed reports of the health of your virtual server. 

Coming to security, it can authenticate users from an Active Directory Domain and the remote connection from clients to host is established via SSH. On the performance front, MS Virtual Server disappointed us. It took a longer time to install both 



Windows XP and PCQLinux. On running Business Winstone, it gave a score of 8.8 which is drastically lower than everything else and kernel compilation took around 17 mins 20 secs, which is not so good among the lot.

Xen



In our hunt for the right server virtualization software for your enterprise, we came across with this nice piece of software that is becoming very popular among Linux Web hosting companies nowadays. It works in a different manner compared with other contenders in the lot. As we have seen VMware and MS VS, do system virtualization whereas this does OS virtualization. That is, the guest OS is ported on top of the host OS and running with a specialized virtualization kernel. This technique is increases the performance ratio of the virtual machines. And that we saw reflected in our test results. Here the reason for performance enhancement is that it doesn't have the Virtual Machine Layer. The guest OS is installed directly on top of the host OS and reduces the overhead created by the VM layer.

But at the same time Xen is not a user-friendly thing and you have to be more or less a Linux guru to make it run properly. But the installation is quite easy and took just around half an hour. We installed it on a PCQLinux 2005 machine and got just two dependency errors. One was about Python and another for Twister. Both of them were sorted out with a single yum update and we were able to boot the machine with the customized Xen kernel (for more details on how to install go through the article at

https://www.pcquest.com/content/linux/2005/105041204.asp). 

From then on, we needed to get our hands dirty. First, we encountered a weird problem that Xen faces with FC3 distros. In FC3 based Linux distros, you don't have the /dev/console file and this is required for Xen to boot. This problem had the virtual

machine to rebooting continuously. After sorting out this problem we figured out that there was a similar problem with the 'udev' service. We managed to solve this by first deleting /dev/null file and recreating it with the command 'mknod /dev/null c 1 3'. Now our Xen was up and running. 

We allotted the machine with the same spec that we gave to all the other contenders for benchmarking and did a Linux Build test and found that it took the lowest time of the lot. And not only this we also tested the guest OS while fully consuming the resources of the host machine and found that the total difference turned out to be negligible (a mere 3 second difference). And that was only due to the fact that we had both the file systems (of the host and the guest) on the same disk. So we can easily say the performance of the VM doesn't get affected by any resource constraint on the host OS. But after all this, the disappointing part of the software is that it can only run Linux and BSD clones as a the guest OS. So no Windows in Xen. Another disappointment was that it can still only emulate x86 32 bit machines. So, while you can install Xen on a 



64-bit machine, it will not use the capabilities of the 64 bit processor. But the next version of Xen is supposed to have SPARC and
64-bit support.

Now comes the manageability part. After using Xen for a couple of days we decided this thing is still rough on its edges and needs a good polish. The configuration is majorly command line based. There is a Web-based interface available, but it refused to run on our PCQLinux 2005 setup. To use that though, you could try with the Xen Live distro, since it has all the components of Xen pre installed and configured. But still this Web-based configuration tool cannot stand in front of the VMware and MS VS management consoles. Overall if your organization needs more performance than easy manageability and you can leverage Linux expertise this thing could be for you. And you obviously should not need to run Windows. ¨