Benefits of Virtualising Citrix?

[JoJoGabor]

Hi Guys,

I've been considering this scenario as I know a lot of people do it but I cant see the real beenfits to virtualising a properly setup Citrix farm and need some ideas if I'm asked to "sell" the idea.

Here are some possible arguments and why I cant see the benefit:

More Servers running one one host: If the Citrix Farm is well spec'd, server resource utilisation should be high, therefore maximising the numbers of users connected.

ABility to VMotion servers between hosts: If the Citrix Farm is large enough, any new connections will simply be redirected to online server. Obviously any current connections will be disconnected though (ONe advantage I guess)

In DR, VMs can be brought online in the DR site: Just have online Citrix servers as part of the farm with zones setup correctly so they are only used in DR

Can anyone think of anything else I'm not considering?

Cheers

[ESXxor]

Well, we are a quite large Citrix hosting shop for end customers, as well as internal users.

In our scenario, we sometimes have customers with custom applications or applications that don't mix well with other applicaitons on the same server. In this instance, we like to create their own virtual Citrix server where we can effectively and easily segregate their apps.

Another great example for us is the ability to snapshot a citrix server before implementing any upgrades etc.

One thing to consider though, ast least for us, is that I believe it to be a myth that you can get more users crammed in to many virtual citrix servers on one host server rather than just haveing a dedicated physical Citrix server. We find that on the latest ESX server with a Dell dual Quad Core system that Citrix starts crapping out at around 20 to 25 users in a virtual server. (We like to keep users around 20 users. ) Even with 10 users in a virtual server the performance is nowhere near as crisp as a physical server... A physical equivalent setup would yeild god knows how many users with excellent performance.

There are still benifits of Virtualization for Citrix Servers though and we pretty much maintain them for our smaller, "Special Needs" customers. All others that run standard applicaitons get lumped into our Physical Server farm.

[MikaA]

We find that on the latest ESX server with a Dell dual Quad Core system that Citrix starts crapping out at around 20 to 25 users in a virtual server.

Is this with 1 vCPU or some vSMP vserver? We've been thinking about using virtual TS servers but mainly because we are just starting to use terminal services and don't have "many enough" physical servers (and I doubt never will) to accommodate all the different application/language needs. So, we thought about creating several 1 vCPU servers to get around that..

[ESXxor]

We have tried both 1vCPU and Multiple and ended up sticking with multiple. Keep in mind, you can have more Virtual Citrix Servers on the same host, but like I said performance is nowhere near a physical server. Still usefull for us and sounds like you too, its just I highly doubt making many Virtual Citrix Servers on a host copared to just a physical server will yeild better results / more users.

In fact, I believe both Citrix and VMware both state high utilization Citrix servers are a bad idea for virtualization.

[MikaA]

Hmm, wasn't/isn't there some VMware whitepaper on this...... yes: . Yes, it their publication and it's based on scripts and they state that real world number of users would usually be lower but still, their results show 100+ users on 1 vCPU machine (Opteron 875 based host) with linear scaling with multiple vservers.. Based on that, I was kind of hoping the real world number of users would be a bit higher than 20 nowadays...

But hey, you apparently have experience/knowledge on how many Citrix users can you have per physical server? If we take a "modern server" (2 QC CPUs) with enough RAM and such, how many basic office users can you serve with it? Everyone always say "well, it depends on the users" but if talking very basic stuff, i.e. web browsing, office software and email, can you give some sort of useful ballpark figure? 100? 200? 500?

[JoJoGabor]

A lot of the time applications such as Office and IE cause more problems with memory. If you think every instance of OUtlook could easily use 50Mg RAM and IE can easily use 100Mb, your Ram is going to run out quickly.

I've seen older dual-core machines host over 100 concurrent users when using small footprint apps like telnet sessions.

But as a complete guesstimate with a physical server with 8 cores and lots of RAM running Office etc, I reckon you could get 20 users per core. 160?