The most common problem with VHDs occurs when the disk of a virtual server is full. The nice thing about virtual disks is that they are quite easy to expand. I can’t help but wonder why Microsoft’s virtualization solutions haven’t integrated this option. In theory, this should be possible even while the server is running. After all, it is no problem to defragment the disk of a running server, so why shouldn’t it be possible to resize an online VHD?

In any case, VHD Resizer is free and easy to use. One thing to remember is that you have to shut down your virtual server first. All you have to do is to tell VHD Resizer the new size, and the name of the new virtual disk. VHD Resizer supports fixed disks (disks with an unchanging physical size) and dynamic disks (disks that grow dynamically). It seems as if the tool also supports conversion from dynamic to fixed disk types and vice-versa, but this didn’t work in my tests. Enlarging a VHD, however, worked fine.

VHD Resizer changes the size of the VHD, but not the size of the NTFS partition. Thus, if you access the VHD through a virtual machine, you just see a larger disk with additional unpartioned space. You have to use a partition management tool, like diskpart, to extend the partition. Only then can you make use of the full capacity of the virtual disk. Diskpart is a Windows command line tool.

Extending a partition with diskpart is very simple:

1. Launch diskpart on a command prompt.
2. Type “list volume.” This gives you the number of the volume that you want to extend.
3. Type “select volume volume-number.“
4. Type “extend.”

Note that Microsoft’s documentation for diskpart states that only the extension of data volumes is supported. System or boot volumes may be blocked from extension. Even so, during my test, I was able to extend a Windows 7 system volume without problems. Still, it might be safer to add the VHD to another virtual machine as a data volume and extend it there.

By the way, if you only want to enlarge a data volume, you don’t need VHD Resizer. Just create another virtual disk with the appropriate size for your virtual machine, and then copy all files to the new disk.

VHD Resizer

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When I first tried VirtualBox I thought it was not much different than Virtual PC. Only when I used it for a while did I find out that it has some essential features that Virtual PC lacks, as described below:

Multiple snapshots

One of the biggest advantages of running software tests in a virtual environment is that you can create a snapshot of a stable configuration which allows you to go back to that point in time if you mess up your system. Virtual PC 2007 SP1 has an undo function which can be considered as a single snapshot. VirtualBox supports multiple snapshots. This way, you can save states of your virtual machines the same way you store different versions of a text document. You can also create snapshots while the virtual machine is running. Virtualbox’s snapshot feature is as powerful as VMware Workstation’s.

64-bit guest support

It is hard to believe but Virtual PC 2007 SP1 doesn’t support 64-bit guest operating systems. You can run it on a 64-bit host, though. VirtualBox supports 64-bit hosts and guests. You probably know that there is no 32-bit version of Windows Server 2008 R2. Thus, Virtual PC is no option if you want to try Microsoft’s latest server operating system. I ran Windows Server 2008 R2 on VirtualBox and it worked fine; just the virtual machine additions are not yet supported. This also applies for Windows 7. Basically, this means that there is no clipboard support (you can’t use copy and paste text between host and guest) and there is no seamless mouse integration (you have to press STRG to leave the VM with the mouse pointer). You might also recognize slower video output without the guest additions. I hope the next release will bring this feature.

Support for Linux, Mac OS X, FreeBSD, OpenBSD and Solaris as guest OS

Virtual PC supports only Windows as guest OS. There is an emulation for the PowerPC-based Mac OS X, but as far as I know you can’t run the x86 edition. You might be able to get Linux running on Virtual PC if you are a geek. But many report problems and it is not officially supported. VirtualBox on the other hand isn’t that choosy about the guest OS. If you like to look beyond the Windows horizon every now and then, then VirtualBox is certainly the better choice. Moreover, VirtualBox can be installed on Windows, Apple OS X, Linux, and Solaris.

Performance

I didn’t measure the performance difference between Virtual PC and VirtualBox myself. However, I have read several times that VirtualBox is faster. Tim Anderson compared the performance of VirtualBox 1.5.5 and Virtual PC using the PassMark suite and found that VirtualBox is about 50% faster than Virtual PC. The current edition of VirtualBox is 2.1.0. It is possible that the difference is even bigger now. Especially when you run multiple guests performance is an important factor even if you are only testing. (The Mars Box has a comprehensive performance comparison between VirtualBox and VMware Workstation.)

Remote Virtual Machines (RDP support)

If you have your virtual test environment on a remote server, then you will like the VirtualBox’s VRDP feature. VirtualBox has a built-in RDP server (VRDP) which allows you to connect to virtual machines with any RDP client. This is especially useful if your test environment uses private IPs and NAT because you can use the host’s IP for the RDP connection. To avoid conflicts with the RDP server of the host it is advisable to change the RDP port of the virtual machine. Each VM can have its own unique RDP port which allows you to connect to multiple VMs simultaneously. Note that the guest’s RDP server doesn’t have to be running. This should work even if the guest OS is Linux. I didn’t try this, though. Another cool VRDP feature is that you can access local USB devices within the virtual machine that runs on a remote server.

VHD and VMDK support

VirtualBox has its own disk format VDI (Virtual Disk Image), but it can open Microsoft’s VHD (Virtual Hard Disk) format and VMware’s VMDK (Virtual Machine Disk File) format. You don’t have to import or convert virtual disks to load a third party virtual machine. This can be useful, if you already have virtual machines that you want to continue using with VirtualBox. Furthermore, it is possible to evaluate Microsoft software through its pre-configured VHDs . At least, this is the theory. I tried to launch two VHDs with VirtualBox on a Vista x64 host and it failed to open with the error message invalid pre-header. Sun already knows about this bug and it should be fixed in the next version. I was able to open a VMDK file that I created with VMware Workstation 6.5 in VirtualBox, but older VMware virtual machines did not boot up. I suppose there are ways to get these VMs running too. However, you probably have to invest some time.

I didn’t discuss all the VirtualBox features that Virtual PC lacks (for example, multiple monitor support for the guest, or the ability to install VirtualBox on a GUI-less host), but it should be clear by now that VirtualBox is the more powerful virtualization solution.

Note that there are two editions of VirtualBox, an Open Source version and a commercial version. The commercial version is free of charge for personal and educational use. Commercial use for individuals within a company is also free if no more than one client connects to the host at a time.

The Open Source edition is released under the GNU General Public License (GPL) and lacks these features: RDP server, iSCSI support, Gigabit Ethernet Controller, and Serial ATA Controller.

The only feature I really miss in VirtualBox is the ability to create linked clones. It is the only reason that I stick with VMware Workstation. Linked clones are copies of a virtual machine which only contain the changes made to the guest. This reduces the storage space significantly if you work with many virtual machines. However, if the decision is between Virtual PC and VirtualBox, the better choice is obvious.

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Whenever I open Virtual PC 2007, I always think that I accidently started the wrong application. Its GUI is a tiny window with only a few menus offering a handful of options. It is hard to believe that this is the main competitor of VMware Workstation. Anyway, it is free and it is from Microsoft so it deserves a closer look.

The first thing, I found strange, is that I wasn’t able to find a function that allows me to import a virtual VMware machine. How can you compete with the market leader this way?

Creating a new virtual machine is easy, since the wizard doesn’t offer many settings, anyway. I wanted to change the amount of RAM to 1GB for my VM, but Virtual PC informed me that my host doesn’t have enough free memory. My PC has 3 GB RAM, 1 GB was being used by a VMware Workstation VM, so I had 2 GB RAM left for my host and the new Virtual PC VM. Strange!

So I installed Vista with only 512 MB RAM using the DVD. Installing a new operating in a VM always means heavy hard disk usage. This usually impairs the performance on the host machine, significantly. However, this didn’t happen with Virtual PC 2007. I think that VMware Workstation 6 Beta3 (with disabled debug mode) didn’t perform so well when I installed a Vista in a new VM. This, however, is just my impression.

Vista was working without any problems in my Virtual PC VM. I only played a little with it, though. Even with only 512 MB, my VM’s performance was OK. However, my hard disk was kept quite busy.

The most important new feature certainly is the Vista support as host and guest. The Virtual PC guy listed all new key features:

• Support for x64 Windows as a host operating system
• Support for hardware virtualization support
• Support for Windows Vista as a guest and host operating system
• Support for PXE network booting of virtual machines
• Support for the use of fullscreen virtual machines on multi-monitor systems (VM still stays on just one monitor though)

Well, in my view, there are no new revolutionary features. I am still missing snapshot management, linked clones and the virtual network settings that I’ve known from VMware Workstation. Maybe the main rival product is not VMware Workstation, but VMware Server because it also for free. I would still prefer VMware Server.

The only reason, I can think of, for using Virtual PC 2007 is that it fully supports Vista. VMware Workstation 6 also supports Vista, but it is only in beta now. However, it makes a stable impression to me. If you disable the debug mode, the performance is OK, too. I somehow think that the final will be released very soon. So at the moment I don’t see any reason to use Virtual PC 2007. If you don’t want to spend money for virtualization software, you better work with VMware Server. If you often test software in a virtual environment, I recommend VMware Workstation. It is certainly worth your money.

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At first, I tried installing Virtual PC 2007 on my Windows testing server. I was quite surprised when the setup program informed me that this host operating system is not supported. What? Can”t install Virtual PC on a Windows Server 2003? That’s unbelievable!

I, then, googled a little and found out that Virtual PC does support Windows Server 2003, but only its Standard Edition. My testing server runs Windows Server 2003 Enterprise Edition. Since I am often working with multiple virtual machines at the same time, I need more than 4GB RAM.

I should have stopped my test at this point, because Virtual PC 2007 is useless for me, if not for my curiosity. So I installed it on my desktop running Windows XP. Afterwards I imported a virtual machine originally installed on Virtual Server 2005.

To my surprise, Virtual PC was complaining again: “The hardware standard (Virtual Server 2005) for virtual machine “test” is not recognized.” I was able to boot up this virtual machine anyway, and it seemed to work fine during my short test. Still I find this message a bit strange and unsettling. Okay, no more googling now. Test is over.

You still want to know about the new features of Virtual PC 2007? Well, it supports Vista as host and guest. That is the minimum I expected. Another new feature is the so called hardware-assisted virtualization. This means that the virtualization technology from Intel and AMD is now supported.

If you are a heavy software tester, then VMware Workstation still is by far the best choice. Linked cloning, snapshot management and virtual networks are must-have-features then. I hoped that Microsoft would catch-up with VMware Workstation 5.5, but you really can’t compare it with Virtual PC 2007.

Maybe, my review is a bit unfair. After all, Virtual PC doesn’t cost a cent. If you only test a tool every now then which you don’t want to install on your desktop, then Virtual PC 2007 is sufficient. VMware Server might be a better option, though. It is also free and a more professional tool. However, it can’t be installed on Windows XP/Vista. You need a server OS as host. See comments below!

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