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Thin Client and Virtual Machines Thread, Citrix VMware in Technical; We have 8GB 64bit (2x quad core Xeon) blade server with FC SAN. I need more Citrix capacity, citrix are ...
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    Citrix VMware

    We have 8GB 64bit (2x quad core Xeon) blade server with FC SAN.

    I need more Citrix capacity, citrix are 32bit 2003 servers.

    Is it worth virtualising the citrix farm and putting TWO citrix servers on one blade sharing one quad core proc per TS, or better to have one TS per blade ?

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    Netman's Avatar
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    I guess it would depend on the sort of loads you're talking about. I would probably lean towards 2 virtual per blade and splitting the load between them rather than one per blade with a larger load. Maybe try it on one and see what sort of response times you get? I think you'd pretty easily get two on that spec of hardware - one would be wasting a lot of the hardware resources available I'd have thought...

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    Thanks, We bought the server as a replacement for some aging hardware, and weren't going to use it for citrix. Unfortunately our load has increased by 30-40% this year due to the way IT lessons have been scheduled and we desperately need the extra capacity.

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    Studies show that VMWare-ed Citrix servers can be a lot less efficient than those based on 'real tin'. Therefore it is not advised.

    Citrix XenServer can supposedly virtualise a XenApp server with only a 10% hit. This is due to the huge amount of work that they have put into the Xen hypervisor for this purpose. Even if you do virtualise, yu still only put a single XenApp server onto a single box - it is purely meant for ease of provisioning and HA.

    You would be better off restructuring your XenApp farm. I assume that you have not gone 64-bit because of certain legacy apps - 64-bit can increase server capacity on its own over 32-bit (I still need to make this move and prove the theory but haven't yet due to time constraints).

    If you do still require use of legacy apps, you could adopt x64 Windows on all but one of your servers and then install just those apps that are 32-bit-only on the remaining one. These legacy apps could then be published to the x64 servers through seamless windows and the end users would know no difference.

    Alternatively, you could do as I have just described and publish the legacy apps using Application Streaming which may have advantages - again, I haven't had time to play with this.

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    Quote Originally Posted by Ric_ View Post

    Citrix XenServer can supposedly virtualise a XenApp server with only a 10% hit. This is due to the huge amount of work that they have put into the Xen hypervisor for this purpose.

    Are you sure that this isn't because of the paravirtualisation that xen offers, I was under the impression htat Citrix rushed it out soon after acquiring xen.

    I been doing some research, and found some papers of examples of multiple citrix/vmware implementations that look quite promising :

    http://download3.vmware.com/vmworld/2006/tac9728.pdf

    this study (paid by vmware) shows that the number of users supported scales with the number of vmware machines added.
    http://www.vmware.com/pdf/esx_citrix_scalability.pdf

    I'll give it a try next week.

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    Ric_'s Avatar
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    Quote Originally Posted by CyberNerd View Post
    Are you sure that this isn't because of the paravirtualisation that xen offers, I was under the impression htat Citrix rushed it out soon after acquiring xen.

    I been doing some research, and found some papers of examples of multiple citrix/vmware implementations that look quite promising :

    http://download3.vmware.com/vmworld/2006/tac9728.pdf

    this study (paid by vmware) shows that the number of users supported scales with the number of vmware machines added.
    http://www.vmware.com/pdf/esx_citrix_scalability.pdf

    I'll give it a try next week.
    I assumed that you would be using ESX/ESXi to virtualise.

    I would be skeptical about those test results. I'm not sure that CPU utilisation is a good measure of performance... no mention is made of RAM utilisation - RAM is the first thing to get used up in a production environment.

    With 8GB of RAM I don't think you will see much success. Go x64 instead.

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    I would back Ric. Virtual TS servers I feel are not the way to go. You would get better performance from physical tin.

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    A 64bit conversion is going to be too epic right now, there are sooo many applications to test.
    I'm between a rock and a hard place, the new machine was bought to virtualise something entirely different. Bad planning has forced this. I think I'm going to do some live 'testing' and see how things work out. It is so quick to provision a new citrix virtual server, and I need to get something sorted soon - either that or shove a citrix server onto the older (5yrs) servers that I was hoping to bin or waste 4GB RAM.

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    Are you using 2003 Enterprise or Standard? Standard is limited to 4GB RAM, Enterprise would be able to utilise your 8GB RAM without having to go 64 bit? Ifnact you could even double it to 16GB for more headroom.

    In my experience (with several 4GB TS's) TS sessions tend to become ram limited before anything else.

    Or am I barking up the wrong tree?

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    Quote Originally Posted by Butuz View Post
    Are you using 2003 Enterprise or Standard? Standard is limited to 4GB RAM, Enterprise would be able to utilise your 8GB RAM without having to go 64 bit? Ifnact you could even double it to 16GB for more headroom.
    They are standard edition servers, in any case the PAE switch doesn't work so well on terminal servers because the 32bit kernel can only handle a limited amount of RAM and only certain application can use the extended memory, TS isn't one of them. PAE might help by preventing some of the application data from being paged I suppose.

    I built the virtual citrix servers (by cloning an existing machine). One thing I can say is that it is pretty quick to provision a new server this way!

    So far the load is looking pretty well distributed. I'm using the 'advanced' metric (page swaps seem to be high on all machines). The virtual server appear to be coping as well as the real servers, currently taking double the number of connections. Will keep monitoring.

    btw the 'number of page swaps per second' does seem to be very high on all servers regularly at 100% using hte citrix 'advanced' load monitor. how does this compare to your TS's

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    Butuz's Avatar
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    Is the Citrix one comparable to perfmon? I am not using Citrix you see, just vanilla Win2k3.

    So your saying running on Win2k3 Enterprise with 8GB of ram won't actually give TS sessions an extra 4GB? If so - thats an eye opener!

    In that case looks like VMWare could be the way to go - dump 16GB of ram in your server and then allocate as much ram to as many vitrual machines as you need!

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    Quote Originally Posted by Butuz View Post
    So your saying running on Win2k3 Enterprise with 8GB of ram won't actually give TS sessions an extra 4GB? If so - thats an eye opener!
    Yes, as I understand it the TS application runs in part of the kernel space and this is actually limited to 2GB RAM. The PAE switch may help for some applications, and might reduce the amount of swapping if a user fires up a bunch of apps at once, but it doesn't help in increasing the number of sessions. The 3GB switch makes things worse by reducing the amount of kernel space. 64 bit is the way forward with memory usage.

    The question is whether the PAE switch will help reduce the number of page swaps more than virtualising 2X servers onto the same phyical machine.
    So far the VM is holding it's own, but I couldn't say if it was the best use of resources.
    Most I've seen today is about 40 users (split between two machines) on one physical, compared to 23 users on a physical machine (dual 3.2GHz xeon 3GB RAM)

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    Be careful with PAE, testing is required when/if you use it as it may actually reduce the performance of the system. As per the Microsoft Terminal Services Sizing Guide.

    Quote Originally Posted by Microsoft
    However, if a terminal server is limited by CPU performance and not by memory, PAE could have a slightly negative effect. Enabling PAE on a system where the CPU is the bottleneck leads to a slight performance decrease of 2% to 6 %
    Or cause the system to become restrained by lack of kernel memory. Systems with PAE enabled require double the amount of kernel memory to track user space memory allocations (due to the memory address translation). Enabling PAE does not give the system access to more kernel memory space (It stays at 2Gb). However W2k8 Server has a feature called Dynamic Kernel Address Space. It doesn't entirely solve the problem, but it will help a lot.

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