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  1. #1
    Join Date
    Oct 2007
    Northampton, UK

    VPS resource isolation


    I'm surprised how many posts there are along the lines of "They cancelled my account for over utilization ..."

    I was under the impression that Xen and VZ could isolate resource usage by guests pretty well but maybe this is not the case.

    Does anyone know how well cpu, memory, disk IO and network traffic are isolated in the different virtulization technologies.

    Are the providers that are having these problems just not setting up their environment very well or is it just not possible to isolate guest resource utilization that well yet?

    Thanks - Matt
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  2. #2
    Join Date
    Jul 2003
    Waterloo, Ontario
    We're currently using AppLogic from 3Tera and it provides us with complete isolation so we can't oversell our servers and all the resources are guaranteed to be there. This includes CPU, RAM and Disk. I could be wrong about this, but Xen also has this feature.

    We've been trying to find new ways to keep testing the grid so if anybody has any suggestions, feel free to PM or email me. We've been testing out cPanel servers, game servers and various other applications.
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  3. #3
    Join Date
    Nov 2005
    Michigan, USA
    Xen has this feature for Disk space and Memory, but CPU and Disk I/O it does not.

    Think about how much your paying and what your getting, if your using 100% of one of their CPU's and you only have a 512MB VPS, then they have to think of their other users on that machine.

    This is a problem with Equal Share, they do not limit your CPU usage, you get an equal share of the CPU. Therefore if you are constantly using more than your share, you will get suspended. This is also a reason why $30 VPS's will benchmark over 200 scores in the unixbench because they can utilize lots of CPU.

    However since you weren't utilizing dedicated CPU, this is what can happen.

  4. #4
    Join Date
    Feb 2006
    New York, NY
    Disk I/O is really hard to limit, on HyperVM - you can set CPU limits with OpenVZ. It saves us a lot of hassle, especially when customers tend to use a lot of CPU - we can just work with them to set a cap on it. I also find it kind of harsh that company would totally cancel an account for over utilization, I would think they would dispatch an email, and then if the matter was that serious - they would just turn off the VPS until they resolve the matter, not delete / cancel it.

  5. #5
    Join Date
    Feb 2007
    Rapidvps did their own customization to achieve isolation. There's an old thread somewhere here on WHT where Rick explained what he did.
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  6. #6
    Join Date
    Jan 2004
    Virtuozzo 4 includes disk I/O priorities and the very latest kernel also had an option to disable fsync operations inside a VPS -- this prevents a single VPS from causing many processes to enter the Disk-Wait state.

    Other than that we personally use CPU Units (proportional share system for dividing CPU allocation based on priorities) and CPU Limit (cap of total % of CPU used -- % is based on plan). There is also a limit on how many CPU's a VPS can see. Most CPU QoS issues are due to misconfiguration under Virtuozzo. Virtuozzo 4 also includes a "burstable" CPU option where VPS's can burst to the full system for a few seconds before they get limited to their CPU Limit. This means they are not hurt for quick bursts, but excessive usage get limited.
    Matt Ayres -
    Linux and Windows Cloud Virtual Datacenters powered by Onapp / Xen
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  7. #7
    Join Date
    Apr 2007
    New York
    Most host's usually give you Gauaranteed stuff. The biggest thing that i see is that they "share CPS" so that it is equal. Most places also put in their TOS that if you use over 25% of the cpu for 15 seconds for say, they will suspend you.

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