stressfree - xen

Fixing slow IDE drives in XenExpress

David — Tue, 23 Jan 2007 03:39:35 +0000

A few days ago I wrote about how XenExpress was an exciting Xen distribution that was hindered by a few little bugs. In my case my IDE drives performed very slowly because DMA flags were not being set correctly. This was caused by the fact the generic-ide kernel module had been compiled directly into the Linux kernel (rather than being left as a module).

Thanks to a tip from Partha Ramachandran on the XenSource user forum I added ide0=0 ide1=0 to /boot/grub/grub.conf which stopped generic-ide from grabbing the two IDE channels. This allowed the amd74xx module to correctly connect to and configure the drives.

The only downside in this process was that /dev/hda and /dev/hdd became /dev/hde and /dev/hdh. This caused issues in the boot process as initially the kernel became aware of /dev/hda and expected it to still be present on the system. To get around this problem I changed the root=/-main flag in grub.conf to root=/dev/hde1 and the same in /etc/fstab. This meant the relevant line in /boot/grub/grub.conf went as follows:

module /boot/vmlinuz-2.6.16.29-xs3.1.0.289.2650xen root=/dev/hde1 ro console=tty0 ide0=0 ide1=0

Whilst the root partition in /etc/fstab was defined as:

/dev/hde1 / ext3 defaults 1 1

After a reboot all went well. Both drives now operate at decent speeds and the whole system is noticeably faster.

linux
xen

XenExpress - the fast lane of Xen virtualisation

David — Sun, 21 Jan 2007 04:19:54 +0000

The open source Xen virtualisation suite has caused a bit of a stir within the Linux world because it combines the power of VMWare without the proprietary code and cost hassles. Unfortunately Xen is not the most user friendly thing in the world to setup or configure. For a large organisation this is not so much of a problem because they can afford to hire expensive consultants or train their in-house staff. For smaller players or individuals interested in the concept but unwilling to invest hours into training XenSource have released XenExpress.

XenExpress fits on a single CD and can be downloaded without charge from the XenSource website (they do however ask for a few contact details). To setup your very own Xen host you just boot the computer from the CD, answer a few configuration questions like time and network setup and then just sit back and watch as XenExpress turns your computer into a fully functional Xen platform (for further instructions checkout this howto). After installation is complete configuration of the Xen host occurs remotely via a Java desktop application that runs on Windows, Linux or after a little hacking OSX. Most of the basic Xen tasks like virtual instance management and system maintenance can be accomplished through the interface without much effort or reference to the user guide. If you are an advanced user you can also bring up a terminal on the Xen host and run your normal Linux commands as at its heart XenExpress appears to be a slimmed down Red Hat distribution.

The XenServer Client on Windows displaying the properties of an instance

XenExpress is a free product and as such it is digitally handicapped when compared to its more expensive siblings. From a hardware perspective only 4gig of RAM is supported which limits the number of simultaneous instances that can be run. At the software level only Debian, Windows and Red Hat instances can be installed from scratch whilst existing Suse Enterprise 9 servers can be migrated onto the server (but not created from scratch).

Installation of a Debian instance is the easiest option as a base copy of the OS is installed on the server ready to use. This means after a couple of mouse clicks and a few minutes waiting a Debian instance will be installed, booted and ready to use. For a new user who just wants to experiment with what virtualisation is all about this functionality is excellent. Experienced users will soon find limitations with this approach but their needs are better meet by the XenServer and XenEnterprise software packages. On a side note existing installations of XenExpress can be upgraded to XenServer through the purchase of a license key which means one can easily shift prototype boxes into production should the need arise without a complete reinstall.

The XenServer client on Windows showing a text console on a Debian instance straight after installation.

In order to run Windows XP SP2 or Windows 2003 you must be using an HVM compatible processor. This rules out Windows virtualisation on anything except for the latest hardware but still its great that such functionality is available in the open source world these days. Another drawback of XenExpress is that it only supports network installations of Red Hat Linux. This means that if you want to run up a Red Hat instance you must first copy your CD media to an FTP or SMB share. This is not a huge pain but it would be nice if you could just install from CD especially given the target market for XenExpress is the casual user. Although I did not try it my guess is Centos will also install using the Red Hat template which means you can run a commercial grade Linux distribution without the commercial licensing fees.

The XenClient on OpenSuse 10.1 displaying some operating statistics of the Xen host

I was really impressed by XenExpress as it made the process of setting up the base Xen host quick and completely painless. I did experience one problem on my test box which was the DMA support was not enabled on the IDE drives. Hopefully these teething pains will be cleaned up as the product matures as things like this will put new users off the product and virtualisation. The XenExpress client interface was very good and quite snappy, I especially liked the fact it combined Text Console, Graphical Console (VNC) and server statistics into a single, well laid out control panel. One major limiting factor with the XenExpress client interface is that is designed to work with a single server rather than operate at a cluster level. Whilst this is limiation is not present in the XenServer and XenEnterprise packages still it would be nice to have the ability to monitor and manage two servers in XenExpress. Going even further it would be really nice to be presented with the option to easily migrate Xen instances between these two servers (through seamless export/import). This would allow even inexperienced users to begin to appreciate the true power of Xen (and hypervisors in general) which is its ability to completely differentiate hardware decisions (i.e. upgrades and retirements) from the operating environment.

At the end of the day XenExpress won't suit you if you are looking for a highly customisable Xen server platform. If on the other hand you are an curious home user or someone looking for a quick and easy way getting into virtualisation then XenExpress is in my view the best way of getting your feet wet. You won't be presented with hundreds of options and in less time that it takes to read and understand the Xen documentation you can have a Xen host with a couple of Debian instances up and running ready to play with.

Sharing disk partitions between Xen instances

David — Sun, 17 Sep 2006 11:20:48 +0000

Picture this, you have your Xen server and a couple of virtual instances configured and you are very happy. That is however until you want two or more of those instances to read or write files from the same disk partition. One way to get around this problem is to use a network file sharing protocol like NFS or CIFS and have one instance operate as a file server whilst the others connect as clients. Sure, a configuration like this works but it requires quite a bit of time to setup and more importantly it drains precious processor cycles as many extra, resource intensive processes must be run.

Steve Wray pointed out to me a clever way of achieving this task with kpartx. This tool works with LVM and creates pseudo logical volumes so that two Xen instances can mount the same piece of disk real-estate. Setting up your virtual file system with kpartx is a lot less work than configuring and testing a network file sharing system, plus it is less processor intensive as the network layer is not required (sharing occurs at the block level). There are a couple of useful howto's describing how to set kpartx up, the most useful one is on the Fedora Wiki whilst it is also mentioned on XenSource's own Wiki.

I personally cannot vouch for this approach but it seems very sensible and if stable would provide a far more efficient virtualised disk sharing platform than network based file-sharing. Hopefully it does prove to be stable and in the future gain support within Xen configuration tools like Novell's. And by the way, am I the only person who thinks it is stupid that Novell's Xen configuration tool can only be run from within an X-Windows session and does not have an ncurses-based equivalent for console users (arguably the majority for production servers)?

The Art of Xen

David — Sun, 12 Feb 2006 19:32:03 +0000

In order to install Zimbra without issues I had to setup Xen on my server. This was actually a good thing because I had been thinking of doing so for a while after experimenting with it last year.

Setting up Xen on OpenSUSE is relatively straightforward if you follow the Xen howto on the Wiki: http://en.opensuse.org/Installing_Xen3

The latest Xen OpenSUSE 10 files can be downloaded from here:
http://www.suse.de/~garloff/linux/xen/RPMs-100/

For my setup I have used the following /etc/fstab file on my virtual server:

/dev/hda1       /                reiserfs acl,user_xattr      1 1
/dev/hda2       swap         swap     defaults              0 0
proc               /proc          proc       defaults              0 0
sysfs              /sys           sysfs      noauto                0 0
usbfs             /proc/bus/usb        usbfs      noauto              0 0
tmpfs             /dev/shm             tmpfs      defaults              0 0
devpts            /dev/pts             devpts     mode=0620,gid=5       0 0
/dev/shm        /opt/zimbra/amavisd-new-2.3.3/tmp       tmpfs   defaults,users,size=150m,mode=777     0 0

I did initally have a lot of trouble setting up the network on the virutal instance but after a lot of experimenting with different Xen packages and configuration options I finally settled on the following file (/etc/xen/zimbra):

# -*- mode: python; -*-

# configuration name:
name     = "zimbra"

# usable ram:
memory   = 512

# kernel und initrd:
kernel   = "/boot/vmlinuz-xen"
ramdisk = "/boot/initrd-xen"

# boot device:
root     = "/dev/hda1"

# boot to run level:
extra    = "3"

# network
nics=1
vif = [ 'mac=aa:00:00:50:02:f0, bridge=xenbr0' ]
dhcp ="dhcp"
hostname="zimbra"

# storage devices:
disk     = [ 'phy:system/mail,hda1,w','phy:system/mailswap,hda2,w' ]

One last thing is that the Xen howto modifies the virtual server's mtab file with the following line:

sed -e "s/^[1-6]:/#\\0/" < ./etc/inittab > ./etc/inittab.new

This command also commented out the default console as well as the other terminal consoles which meant that after installation there was no login prompt. In order to correct this edit the /etc/inittab file on the virtual server (whilst it is still mounted on the host system) and uncomment the following line:

1:2345:respawn:/sbin/mingetty --noclear tty1

Zimbra migration thanks to Xen

David — Sun, 12 Feb 2006 19:22:20 +0000

After the comments from Kevin H about Zimbra to one of my last postings I thought I had better take another look at Zimbra. The last time I downloaded and played with Zimbra was when it was in Beta. It has changed significantly since then and now provides packages for OpenSUSE 10 which is really good to see.

The last time I tried Zimbra I was not too happy to see it installed its own versions of services like MySQL and Postfix. I started a thread on the Zimbra forum back then and it sparked a bit of debate. Unfortunately Zimbra 3.0 still assumes the install system is only going to be running Zimbra which makes it difficult to install on a system already running most of these services. Although I specified different ports to avoid conflicts my test install did not work at all very well and to top it off it managed to break the existing OpenLDAP installation (something to do with missing shared libraries).

Even though things did not work straight off the bat the Zimbra feature overview movie and the little that I had been able to experience had me hooked. Rather than fight the Zimbra install process I decided to setup Xen on the server and provide Zimbra with a clean virtual server to install on. After an evening of toil I finally had my virtual server running fine so I ran the Zimbra installer. Everything installed and ran without issue using the default options and the speed was acceptable given the hardware was now running two instances of Linux, two mail servers and a host of other services. Migrating mail from Hula to Zimbra was problematic as automatic tools such as imapsync do not play nicely with Hula's implementation of IMAP. I eventually resorted to using Thunderbird to copy mail from one server to the other which resulted in the loss of 'Date Received' data. Once the mail was migrated I replicated Hula's mail proxy functionality with fetchmail and switched from a testing to development system without any downtime.

Setting up webmail proxying with Apache was fairly straightforward but it did require a change of the default url for the spellchecker. I posted a question about how to do this on the forum and it was solved within the day. For future reference to change the default spellchecker url use the following command:

/opt/zimbra/bin/zmprov ms SERVERNAME zimbraSpellCheckURL SPELLCHECKER_URL

and then restart Tomcat (or just restart Zimbra).

Like many others I would like to see the Outlook Connector sold as a separate product (with single and pack licenses) so that users of the open source version can get the functionality of Outlook without having to pay for the Enterprise edition. Support for me is not an issue and most of the target install sites I know of are too small to really justify the price of the Enterprise edition (but nearly all use Outlook). I am also holding out for the Zimbra iSync adapter and hoping that this to does not just get bundled into the Enterprise version. It is something I would pay for especially if it lets me add/edit contacts and calendars in OSX and have them synchronised to Zimbra. This would be especially useful to keep all my contacts/calendars in sync across the three Macs I now have (something that .Mac can do but I don't want to pay $200 a year for).

Whilst the web interface is great I prefer native applications because they are (and will always be) much faster and enable offline work to take place. Plus the main reason I use iCal is to easily set alarms in my cellphone so if Zimbra and iCal could work together I can keep my phone reminding me.