Tuning Ubuntu's software RAID

Recently I encountered an issue where the read/write performance of Ubuntu's software RAID configuration was relatively poor. Fortunately, others have encountered this problem and have documented a potential cause and solution here:

The short story is that Ubuntu uses some very conservative defaults for RAID caching. Whilst this may ensure reliable behavior across a range of hardware, it does mean that for many read/write performance will be lacklustre. The solution to this problem is to define a more aggressive caching options on any software RAID partitions that are in use.

USB devices with VMWare Server 2.0 on Ubuntu

One of the nice features of VMWare Server 2.0 is that it supports the forwarding of USB devices to virtual machines. Unfortunately when it comes to Linux the VMWare team have leveraged an old method (/proc/bus/usb) for scanning the USB bus which newer distributions, such as Ubuntu Server 8.04 no longer support.

To resolve this problem the "old" method for scanning for USB devices must be enabled in the underlying operating system. In the case of Ubuntu Server 8.04 this is a case of editing the file /etc/init.d/mountdevsubfs.sh and uncommenting the following section:

# Magic to make /proc/bus/usb work
mkdir -p /dev/bus/usb/.usbfs
domount usbfs "" /dev/bus/usb/.usbfs -obusmode=0700,devmode=0600,listmode=0644
ln -s .usbfs/devices /dev/bus/usb/devices
mount --rbind /dev/bus/usb /proc/bus/usb

Reboot the server and /proc/bus/usb should be functional once more.

Activating a USB device within a virtual machine

Once the underlying USB subsystem is configured the USB device needs to be associated with a virtual machine. For this to occur the virtual machine must have the USB Controller added to its virtual hardware configuration. If the controller is not already part of the virtual machine's configuration shutdown the VM, add the device and restart.

Assuming there are USB devices attached to the server, once the virtual machine boots a small USB icon will appear within the VMWare web management console. Click on the icon and select the relevant USB device to attach it to the running virtual machine.

All going well the USB device will appear within the virtual machine as an accessible device. VMWare Server remembers this selection, so the next time the virtual machine (or server itself) is restarted the USB device will automatically be attached to the running VM.

VMWare Server 2.0 optimisations

VMWare Server 2.0 is emerging as a capable, zero cost alternative to VMWare ESX when used in combination with Ubuntu Server 8.04LTS. Unfortunately "out of the box" performance can be a little disappointing, especially when running guest Windows virtual machines. What follows are a few system tweaks that can improve performance without hampering overall system stability. I have not come up with these myself, instead they are pruned from the following pages:

Kernel parameters

In addition to the default Ubuntu Server kernel parameters, the following should be appended to the end of /etc/sysctl.conf.


Once added reboot the server to ensure their application is successful and permanent.

Create an in-memory temp drive

In the host's /tmp directory create a new directory named vmware (e.g. /tmp/vmware). This will be used as the mount point for a tmpfs (in-memory) partition for storing VM related, temporary files.

Edit /etc/fstab and add the /tmp/vmware partition to your list of mount points:

tmpfs /tmp/vmware tmpfs defaults,size=100% 0 0

Now if you execute the following command the tmpfs filesystem will be mounted at /tmp/vmware:

sudo mount /tmp/vmware

If successful, reboot the Ubuntu server to ensure the tmpfs partition is mounted at boot time.

VMWare Server configuration

Edit the /etc/vmware/config file and ensure the following configuration declarations are set:

prefvmx.minVmMemPct = "100"
prefvmx.useRecommendedLockedMemSize = "TRUE"
mainMem.partialLazySave = "TRUE"
mainMem.partialLazyRestore = "TRUE"
tmpDirectory = "/tmp/vmware"
mainMem.useNamedFile = "FALSE"
sched.mem.pshare.enable = "FALSE"
MemTrimRate = "0"
MemAllowAutoScaleDown = "FALSE"

These configuration declarations instruct VMWare Server to keep all virtual machines in memory and not to write unused blocks to disk. It also sets the temporary directory to the newly created tmpfs partition at /tmp/vmware.
Restart the VMWare Server process (sudo /etc/init.d/vmware restart) or reboot the server for these changes to take effect. The net result should be notably smoother virtual machine performance, especially when it comes to Windows guests.

Virtual machine tips

  • Always use fully allocated disk images.
  • Do not use snapshots as they are approximately 20% slower.
  • Always install the VMWare Tools package.
  • If running Linux make sure the kernel is compiled for running within a VM, or is using the correct boot time parameters.


VMWare Server 2 finally goes gold

On September 23 after a year of public development VMWare Server 2.0 was officially released. Server is VMWare's free, entry-level, server-centric hypervisor. Unlike VMWare's other server virtualisation products ESX and ESXi, Server must be pre-installed onto a host operating system (Windows or Linux). This adds a management and performance overhead, which for some is incentive enough to choose VMWare's more costlier offerings (or explore Xen). However if you are looking to easily virtualise a handful of servers and do not mind a small performance hit, VMWare Server is a great place to begin.

In comparison to VMWare Server 1 (a.k.a GSX) this new release appears to be a complete rewrite. However when first announced the new version received a mixed response as many existing users viewed it as slow, bloated and buggy compared to its predecessor. Ignoring the bugs which come with any beta-quality code, the majority of this criticism fell into two areas: the new web-based management console and a 500MB+ download (up from ~100MB).

Web-centric virtualisation management

Without a doubt the most controversial aspect of VMWare Server 2 is its focus on a web-based management console. In the previous release management was primarily conducted through a Windows-only client with a token web interface provided to view what was running. This new interface enables all of the hypervisor's functionality to be managed and monitored from any modern, Javascript-enabled browser. The only cavet being that virtual machine console access requires an ActiveX or Firefox extension (Windows/Linux only). Process-wise this is a little disjointed as a browser restart is needed when this extension is first installed. Whilst not a major problem this two-step process does take the shine from being able to manage your virtual infrastructure from 'any' computer.

As an aside given the variety of Java-based SSH, VNC and remote client applets it is a little surprising to see VMWare go the ActiveX/Firefox extension route. Whilst I have not tried the ActiveX control, the Firefox extension is large and feels sluggish when running in both Windows and Linux. Still the ability to setup and manage VMWare from something other than Windows is a definite bonus. However as an OSX user it would be nice to see VMWare management support on this platform as well.

Building a webcam with an old laptop, Canon camera and Linux

Recently I put together a webcam for the Aorangi Ski Club's lodge on Ruapehu. The system consists of a second-hand laptop, an old Canon camera and Ubuntu Linux. Images are automatically captured every hour, timestamped and posted to Flickr. The end result is a pretty impressive looking Flickr slideshow.

To put a similar setup together follow these steps.

Step 1: Get the gear

Find a Linux compatible laptop and a Canon camera compatible with the Capture software.

Clueless Linux pundit of the week

There was a posting on the Linux forums that caught my attention mainly because its title and subsequent logic was so twisted that it was hard to ignore. Why Ubuntu Got It All Wrong is a fairly lengthy posting about how Ubuntu Linux, arguably the most successful Linux of the last few years, is completely wrong and should be viewed as a dismal failure. It is an interesting concept, Ubuntu is certainly showing signs of being too popular too fast, but the logic behind the argument is wrong. The weirdest statement made is that a 'revolutionary' Linux desktop should not resemble the current desktop (i.e. Windows/OSX) at all. In fact in the eyes of the author Ubuntu seems to fail because it is too conventional and the money invested by Mark Shuttleworth would have been better spent on experimental, never to be seriously adopted concepts like Project Looking Glass.

Ubuntu on PowerBook

I formatted my hard drive today and repartitioned it with space for OSX and Ubuntu. Originally I planned on putting in a larger hard disk but cracking open an aluminium PowerBook is like tackling a lobster with a butter knife.
Ubuntu installed effortlessly on the machine with very little input from myself. I was even surprised to find my Apple bluetooth mouse works without having to do anything. Apparently the wireless will not work but that is because the wireless manufacturer uses a closed source driver.