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  1. #1
    Join Date
    Aug 2010
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    * How to calculate needed memory needed for a XEN VPS

    Hi,

    Is there a way to calculate the amount of memory a XEN VPS should need to run properly?

    I want to transfer everything from a vps with about 100 domains on it to a XEN VPS... 80% of those domains are CMS like Joomla ... just regular web hosting and some reseller hosts... The server i will be using is an i5 intel with 6Gb memory... There is already 2 other VPS on it... 1024 mb ram each. I will install cPanel, VPS accelerated version ( i know i need about 512 mb only for cPanel to run properly).

    How to calculate those things? Is there any way?
    Last edited by martin33; 03-30-2011 at 12:03 AM. Reason: Forgot to mention i will install cpanel

  2. #2
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    Quote Originally Posted by martin33 View Post
    I want to transfer everything from a vps
    Clarification (sorry!) i want to transfer everything from a dedicated server

  3. #3
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    With that many Joomla sites, 4 gigs of RAM should be a good safety net.

    FYI, I've seen people get their VPS Optimized cPanel install to run on 95 megs. Mine's only using about 150 megs RAM (SpamAssassin can be RAM hungry).

    Get 64 bit CentOS as well, so you can take advantage of the higher Memory buffering capabilities.
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  4. #4
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    Aug 2010
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    Hi,

    I know you can base this on experience... but... do you (or someone else!) know a good way (math equation ) to calculate the needed memory on XEN?

    I heard about things related to busted ram... if i understood correctly, this seems to be overselling... how does this work exactly?

  5. #5
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    Quote Originally Posted by martin33 View Post

    I heard about things related to busted ram...
    Burstable RAM is only available in OVZ not XEN.

  6. #6
    Well, for a start, Xen behaves exactly like a dedicated server (for most intents and purposes anyway Therefore, why don't you simply examine the memory usage on your current server and this will give you a good idea of what you need your virtual server to provide?

    If you use cPanel you can view the current memory within WHM or you can log in via ssh and run the command "free -m". From there, you can make a more accurate assessment of how much memory you need.
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  7. #7
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    Quote Originally Posted by RavC View Post
    Well, for a start, Xen behaves exactly like a dedicated server (for most intents and purposes anyway Therefore, why don't you simply examine the memory usage on your current server and this will give you a good idea of what you need your virtual server to provide?

    If you use cPanel you can view the current memory within WHM or you can log in via ssh and run the command "free -m". From there, you can make a more accurate assessment of how much memory you need.
    Lol : this was too simple... i didn't thought about it... i was trying to find a way to calculate something i have in front of me am i getting with this change???

    I must say because i am new to vps, i am a bit nervous doing this change... affraid to wake up on the morning, see everything crashed... readed the horor story of what happened to HyperVm users last year (thousans of deleted vps due to security issues)...

    ...i am not using HyperVm, but... still nervous about this change... want to do it, but don't want to get into troubles! (in fact, i do not have the choice.. otherwise, i will need to purchase 2 other servers, and i really do not want to afford this).

  8. #8
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    FYI if someone else is wondering if you can easily figure out that stuff as with a dedicated server... ...found this in the xen documentation :

    "It is difficult to credibly present hypervisor performance statistics as there are multiple benchmarks available which are not universal in the methodologies and metrics. Instead, I will highlight some of the ways that the Xen hypervisor is fundamentally lowering processing time, memory usage, and networking efficiency."

    ...et voilą! it says everything :-)

  9. #9
    Join Date
    Aug 2010
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    Wooo...

    Here is the output...

    Total : 7967
    used : 7867
    free : 100
    shared : 0
    buffers : 244
    cached : 6806
    swap : 2055 (total) 0 (used) 2055 (free)


    Do you think it should be a good idea to transfer this to a VPS?
    Last edited by martin33; 03-30-2011 at 03:21 AM.

  10. #10
    Join Date
    Jan 2004
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    593
    #free -m

    What is the -/+ buffers/cache line stating for used and free?

  11. #11
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    Aug 2010
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    *

    Getting confused...

    free -m ssh command outpu i only have 100 mb free memory

    but...

    WHM says :

    System information
    Server load 0.00 (4 CPUs)
    Memory Used 10.38% (846812 of 8158936)
    Swap Used 0.01% (116 of 2104504)

    On wich of those stats should i base my idea?

  12. #12
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    Quote Originally Posted by speckl View Post
    #free -m

    What is the -/+ buffers/cache line stating for used and free?

    -/+ buffers/cache: 815 7151 i prefer this output

  13. #13
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    The second one is what you're actually using. The free command includes cache in memory usage.
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  14. #14
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    2gb ram vps should be sufficient.

  15. #15
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    Yeah... that's what i can see...

    What about the processor... is it possible to configure the processor speed using xen? How it works exactly?

    On vps.net website, they say, for example, they dedicate a pre-determined speed of cpu...

    is it possible using XEN to do this or with other virtualization technologies?
    Last edited by martin33; 03-30-2011 at 03:42 AM.

  16. #16
    Join Date
    Jan 2004
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    593
    Not sure what your trying to do but it sounds like you're wanting to have your sites on one VPS and sell the other nodes to someone else.

    You can setup the server to share the cpu resources if you wish. The biggest issue with a vps is that you don't know how cpu/disk intensive your neighbors are going to be. One neighbor may require a dedicated server but is hosting on a vps to save money. You just never know your neighbors so you must have a reliable vps provider to handle this for you.

  17. #17
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    Aug 2010
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    Yes, that's what i want to do.

    how can i limit the cpu/disk usage under xen then?
    Last edited by martin33; 03-30-2011 at 03:53 AM.

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