CPU Masking for Citrix XenServer

I don’t usually blog much about Citrix just because I don’t spend much time with it.  This week I ran into a challenge that we occasionally used to run into in the past so I found myself having to do a little Citrix homework for a change.  The challenge is one of CPU differences between XenServer hosts.

Say you’ve got an established XenServer farm setup with 6 hosts that are all identical from a hardware perspective.  With this configuration you can take advantage of all the cool and time saving features that XenServer has to offer like XenMotion – the ability to hot migrate virutal machines between hosts.  But what happens after a year or two when you need to add additional servers to your farm but the servers and in particular the processors you have in the other 6 servers are no longer available?  I won’t go as far as to say “you’re screwed” but you would at least have to create a new farm with the new servers.  This is certainly not the end of the world but you are now managing two farms instead of one and have introduced more complexity to your environment.  All this due to the different feature sets of the different processors – which would proclude you from doing XenMotion across all of your hosts.

This was not only an issue for Citrix users but for VMware users as well.  VMware was a little quicker out of the gate to solve the issue by using CPU “Masking” which essentially dumbs down the newer processor to the same feature set as the oldest processor in the farm hence enabling the vMotion/XenMotion and other features.  There are obviously some restrictions to the types of processors that are compatible – you can’t make an AMD and Intel work together but like vendor processors within a generation or two of each other will usually be ok (check none the less).

So in doing my homework this week I was happy to discover that CPU Masking is now an available feature for XenServer.  This has been out for a few months now I just never looked into it until recently.  To take advantage of the feature you’ll need to upgrade to XenServer 5.6.  Once your there you should be good to go.  This will be very beneficial now that the newer servers are moving from 4-core to 6-core and 8-core architectures.  Using this feature you’ll be able to take advantage of the newer, faster procs and not have to rearchitect and migrate your existing farm around.  There is a pretty good article on the Citrix Community Blog with links to things like HCLs, test kits and other tools.  So check it out at the link below.

http://community.citrix.com/display/ocb/2010/10/26/CPU+masking+support+in+XenServer+5.6

 

 

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