TO-Tech Blog

I’ve long wondered about why Microsoft included a virtual hard drive (VHD) compacting option in its Virtual Server Disk Inspector since it never seems to compact anything when I tried it. So I read the highlighted section on pages 24 and 25 of the book…
Professional Microsoft Virtual Server 2005

…titled Compacting a Dynamically Expanding Virtual Hard Disk with great interest. Ben Armstrong (a Microsoft Virtual Machine Product Manager) has provided a lot of good information about Virtual PC and Virtual Server in his Virtual PC Guy blog. So, his writing is heavily weighted in the valid column when I read what he has to say. However, in this case, I’m still mystified by VHD compacting even after reading this section and especially the Linux related aspects of this section.

Ben recommends zeroing out the Linux VHD free space by creating a file using cat /dev/zero > zero.dat. This creates a file that fills out the unused portion of the VHD. This fills up the hard drive. The next part of the scripts syncs the buffer and then removes the zero.dat file. This means if you have your dynamic VHD set to, say 127GB, you need at least 127GB and maybe 127GB x 2 (double). My test VHD was set to max out at 16GB. So, I didn’t have this problem. I had a lot of free server host hard disk space. I then shutdown the Linux Guest OS before heading over to the web-based Virtual Server management window to start the disk compacting. Here’s the odd result I found.

Size Linux reports used inside the Guest OS: 4.6 GB

Size Virtual Server reports VHD occupies on the host: 9.7 GB

Size of VHD with zero.dat file completely filled: 12.3 GB

The Virtual Hard Disk was a bit over twice the size of the file space Linux reported using. This is normal since this particular virtual machine sees moderate use as a test box. Files get installed and deleted frequently. The size of the VHD completely filled also makes sense although I thought it would get closer to 16GB. Here’s the surprise though. After completing the VHD compacting, the VHD file was 10.8 GB. Yep, compacting the VHD actually INCREASED its file size by 1.1 GB compared to where it was before starting the process of creating the zero.dat file.

Patch Tuesday is always a hassle if you have a bunch of virtual machines running in Microsoft Virtual Server 2005 (R2 SP1). I have my VMs set to Save State when VS2005 detects that the host is power off. The majority of the time (say 60 to 80%), the VMs restart and restore from Saved State. However, a couple of times a year, this doesn’t happen. I vaguely recalled Microsoft’s Virtual PC Guy (Ben Armstrong, Virtual Machines Program Manager) mentioning this in his blog a while back. So, I search his blog and, yep, here’s his blog item…

Problems with Virtual Server when shutting down the host

…that leads to Knowledge Base item 888745…

Guest computer state is not saved when you shut down the host computer on Virtual Server 2005

…which recommends dealing with this by making a change in the Registry (a potentially scary process on a server… be very very careful) that changes the WaitToKillServiceTimeout to 90000. FYI: The default value is 20000 on my Windows Server 2003 R2 Enterprise Edition servers.

Unfortunately, this did not fix the problem for me. All my virtual machines set to save state and then restore from saved state after a reboot restarted after rebooting the host to install Patch Tuesday patches. I then made the registry change described in KB888745 and rebooted the host server again. And, again, all my VMs rebooted instead of being restored from Saved State.

FYI: The expected outcome (restore from saved state) worked when I rebooted for the August Patch Tuesday patches (the September Patch Tuesday patches did not require a reboot).

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UPDATE: In a Homer Simpson Doh! moment it occurred to me that I need to reboot the test server one more time to see if the registry change actually helps. The WaitToKillServiceTimeout would have still been 20000 and not 90000 in the second reboot described above.

If you use Microsoft Virtual PC or Virtual Server and have Red Hat, Fedora, or CentOS Linux guest OSes, you probably have clock problems. Clocks basically lose an alarming amount of time may be hours off within a day or two. You may also have repeating keys problems when typing. Microsoft’s Ben Armstrong (Virtual PC Guy) posted a tip a while back…

Repeating keys under Fedora and Red Hat Enterprise Linux

…that pointed to a Microsoft Knowledge Base (KB) article that recommends adding the clock=pit (programmable interruptible timer) option on the grub kernel line in /boot/grub/menu.lst. However, if you started using RHEL 5 (CentOS 5 in my case), take a look at your /var/log/messages file. You will probably find a warning that the clock= option has been deprecated. From what I can see, replacing it with…

clocksource=pit

…takes care of that warning. However, the RHEL 5 based Linux clock still runs a bit slowly. I ended up having the clock sync with a time source every hour to deal with it.

Microsoft released a pre-built Virtual Hard Disk (VHD) of…Microsoft Windows Server 2008 Beta 3 VHD (Full Installation)

…for download. The download consists of 5 files (CDs). Note that the requirements specifically say Virtual Server 2005 R2 with 1GB RAM allocated to the Guest OS. Unlike Windows Server 2003 R2 which can run reasonably well as a test environment with only 256MB RAM allocated to it, Server 2008 (Longhorn) really needs a lot of resources.

Saw the notice in Mike Walkers blog that Microsoft is providing a SharePoint Server evaluation system in a virtual machine that can be run using Virtual PC or Virtual Server (both free). You can find the VHD (Virtual Hard Disk) download here:

Microsoft Office SharePoont Server 2007 VHD

Changing where Microsoft Virtual Server looks for its Virtual Machines is easy to find and set in its web-based administrative interface. But, I didn’t know it could be set for Virtual PC too until I read a post in Microsoft’s Virtual PC newsgroup pointing to a blog post by Ben Armstrong that talks about the MYVIRTUALMACHINES system variable at…

Changing the default location the Virtual PC uses for virtual machines

I just read Edgar’s interesting comments to one of my previous Vista-related posts and took special note of his 3rd and 4th points where he said:

(3) The system does not come with any discs for the installed software; though I think that a boot disc for Vista can be purchased. Perhaps hard discs are more reliable than my diskette fileing system.

(4) The lack of backup discs makes me leery about trying to install Linux, since that involves changing the Windows Vista partition, always a nervous activity.

Edgar: The last time I bought an HP PC (about 5 or 6 years ago), it came with an option to create recovery discs on a series of CD-R discs. Check to see if your HP has that option.

More importantly though, unless you have some special requirements that requires Linux to have native access to your notebook, you should definitely consider installing Microsoft Virtual PC 2007 instead and use it to run the Linux distro of your choosing as a Guest OS on a Virtual Machine. I’ve used it to run Fedora Core, CentOS Linux (another Red Hat variant), SUSE Linux, and Ubuntu. Virtual PC is free. So, the price is right.