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  • How many virtual machines

    Is there a rule of thumb or some method of calculating how many Virtual Machine instances can run concurrently on a host?

    I have a quad core machine with 8GB of Ram that "gets stupid" with more than 4 VM's started, oddly it does not seem to matter how the virtual machines are configured.

    Thanks

    abe

  • #2
    Re: How many virtual machines

    Originally posted by abesimpson View Post
    Is there a rule of thumb or some method of calculating how many Virtual Machine instances can run concurrently on a host?
    There's both a "rule of thumb" number of virtual machines (4 - 6 rule of thumb VMs per core) and a maximum number of virtual machines that can run on a host (and more clearly the rule defines how many virtual processors can be assigned and powered on per host: 80 on ESX 2.x, 128 on ESX 3.x) and a maximum number of virtual processors that can be assigned to a processor core (eight).

    Assuming an adequate disk subsystem, your host should be able to handle 16 VMs, but your short on memory and you don't tell us how much RAM you have assigned to each VM or whether or not you're overcommiting RAM. Without the proper disk subsystem, your disk will quickly become the bottleneck and you'll have too much disk I/O contention. ESX likes plenty of disk spindles to work with for VMs that are actively reading and writing to their virtual disks.

    Originally posted by abesimpson View Post
    I have a quad core machine with 8GB of Ram that "gets stupid" with more than 4 VM's started, oddly it does not seem to matter how the virtual machines are configured.

    Thanks

    abe
    You'll need to better define "gets stupid" because I don't know what that means. My observation is that your RAM is disproportionate to your CPU cores. Rule of thumb 4GB RAM per processor core. With a quad core box, you should have 16GB RAM minimum.

    Jas
    Last edited by jasonboche; 7th April 2008, 04:43. Reason: spelling mistakes
    VCDX3 #34, VCDX4, VCDX5, VCAP4-DCA #14, VCAP4-DCD #35, VCAP5-DCD, VCPx4, vEXPERTx4, MCSEx3, MCSAx2, MCP, CCAx2, A+
    boche.net - VMware Virtualization Evangelist
    My advice has no warranties. Follow at your own risk.

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    • #3
      Re: How many virtual machines

      You also don't state whether you're using ESX or some other virtualisation product; ESX is the only one I'm aware of which installs on bare metal; if you're using Microsoft Virtual Server on Windows Server 2003 for instance then 4 server VM's in only 8Gb RAM is... shall we say "ambitious"?

      You also don't say which OS your VMs are running...

      We have ESX servers in our server room which are running ten Windows Server 2003 VMs normally (we don't like to go above 12) and they are running on 4x3.2GHz Xeon, 32Gb RAM and Tier 1 SAN storage for all disks. ESX copes quite nicely; our VMs are generally run with (dynamic) 1.5-3GHz of CPU and 1-2Gb RAM.


      Tom
      For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

      Anything you say will be misquoted and used against you

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      • #4
        Re: How many virtual machines

        Originally posted by Stonelaughter View Post
        You also don't state whether you're using ESX or some other virtualisation product; ESX is the only one I'm aware of which installs on bare metal
        XEN, IronBox, xVM, HyperV, KVM
        ________
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        Last edited by DYasny; 6th March 2011, 18:23.
        Real stupidity always beats Artificial Intelligence (c) Terry Pratchett

        BA (BM), RHCE, MCSE, DCSE, Linux+, Network+

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        • #5
          Re: How many virtual machines

          Fair enough but I never heard of any of them LOL - it's not my primary technology area.

          We still don't know what the OP is using...


          Tom
          For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

          Anything you say will be misquoted and used against you

          Comment


          • #6
            Re: How many virtual machines

            First I apologize for taking so long to get back, that of of the way;

            My needs are not server based. I run a home built stock trading system (quite successfully I might add) and I use the virtual environment to isolate each of the running systems.

            The Host computer is not "server" quality;
            The motherboard is an ASUS P5K (I was told that the max RAM that this configuration would run is 8GB)
            OS: WinXP64 on the Host computer
            OS: WinXP32 on each of the individual virtual machines

            Each VM set to 1.5GB RAM

            VMware Workstation 6

            As all 4 machines are running very well, I take it that I am getting more than I deserve from this configuration?

            Comment


            • #7
              Re: How many virtual machines

              No I wouldn't say you're getting more than you deserve but you're getting good mileage out of 1 white box and that's precisely one of the selling points of viritualization. Kudos to you for grasping virtualization technology, lowering cooling and electrical costs, making more efficient use of your physical space, and minimizing the size of your carbon footprint you will leave for this world when you die.

              You still haven't defined "gets stupid" for me yet. What does this mean?

              You're running several VMs concurrently on workstation class hardware with (I'm guessing) no redundancy and you're probably burying the needle on disk I/O on (I'm assuming) a single IDE or SATA disk spindle. Consider a few more disk spindles if you're running into disk I/O bottleneck.

              Jas
              VCDX3 #34, VCDX4, VCDX5, VCAP4-DCA #14, VCAP4-DCD #35, VCAP5-DCD, VCPx4, vEXPERTx4, MCSEx3, MCSAx2, MCP, CCAx2, A+
              boche.net - VMware Virtualization Evangelist
              My advice has no warranties. Follow at your own risk.

              Comment


              • #8
                Re: How many virtual machines

                By "Gets Stupid" I mean all VM's slow down to a point where nothing operates.

                I do have 3 internal SATA Drives installed.
                - The 1st runs the host machine OS
                - The 2nd holds the Virtual Machines
                - The 3rd stores the data in/out to/from the VM's
                - Data is backed up to external drives

                Thanks

                a
                Last edited by abesimpson; 9th April 2008, 03:23.

                Comment


                • #9
                  Re: How many virtual machines

                  Originally posted by abesimpson View Post
                  By "Gets Stupid" I mean all VM's slow down to a point where nothing operates.

                  I do have 3 internal SATA Drives installed.
                  - The 1st runs the host machine OS
                  - The 2nd holds the Virtual Machines
                  - The 3rd store the data in/out to/from the VM's
                  - Data is backed up to external drives

                  Thanks

                  a
                  That's your problem. You're still only using 1 drive for your VM .vmdk files (drive #2). I'll wager disk I/O is getting pinned. You need to spread your disk I/O over multiple drives by using RAID0 or RAID5. Preferably hardware RAID.

                  Also make sure you're not overcommitting on RAM because that will cause swapping which will compound the issues with disk I/O.

                  Jas
                  VCDX3 #34, VCDX4, VCDX5, VCAP4-DCA #14, VCAP4-DCD #35, VCAP5-DCD, VCPx4, vEXPERTx4, MCSEx3, MCSAx2, MCP, CCAx2, A+
                  boche.net - VMware Virtualization Evangelist
                  My advice has no warranties. Follow at your own risk.

                  Comment


                  • #10
                    Re: How many virtual machines

                    So if I understand this properly I should RAID Drive 1 and 2?

                    Thanks

                    a

                    Comment


                    • #11
                      Re: How many virtual machines

                      Originally posted by abesimpson View Post
                      So if I understand this properly I should RAID Drive 1 and 2?

                      Thanks

                      a
                      I'd RAID 'em all together, that way each of your applications/uses benefits from improved disk performance. However, be aware in that scenario, all applications/uses will share the same disk spindles and as such, those applications/uses have the potential to add their own disk I/O patterns into the mix which could interfere with VMware if in fact those other apps are heavy in disk I/O while you are running your VMs. BTW, forget about RAID1 - that will buy you nothing in terms of performance. You get the least bang for your disk purchase buck with RAID1.

                      Jas
                      VCDX3 #34, VCDX4, VCDX5, VCAP4-DCA #14, VCAP4-DCD #35, VCAP5-DCD, VCPx4, vEXPERTx4, MCSEx3, MCSAx2, MCP, CCAx2, A+
                      boche.net - VMware Virtualization Evangelist
                      My advice has no warranties. Follow at your own risk.

                      Comment


                      • #12
                        Re: How many virtual machines

                        I'd RAID 'em all together, that way each of your applications/uses benefits from improved disk performance. However, be aware in that scenario, all applications/uses will share the same disk spindles and as such, those applications/uses have the potential to add their own disk I/O patterns into the mix which could interfere with VMware if in fact those other apps are heavy in disk I/O while you are running your VMs. BTW, forget about RAID1 - that will buy you nothing in terms of performance. You get the least bang for your disk purchase buck with RAID1.

                        Jas
                        Thanks 10^6 for your advice.

                        Based on your comments I will RAID 2 drives and leave the third drive as stand alone for data heavy number crunching/downloading activities.

                        Potentially I will add yet another drive to the mix when the benefits of the new configuration becomes apparent.

                        I'll continue this post with my results.

                        a

                        Comment


                        • #13
                          Re: How many virtual machines

                          Keep in mind that in a RAID 0 configuration if you lose 1 drive you also lose the data on the 2nd drive as well.
                          1 1 was a racehorse.
                          2 2 was 1 2.
                          1 1 1 1 race 1 day,
                          2 2 1 1 2

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                          • #14
                            Re: How many virtual machines

                            and raid1 doesn't improve performance
                            ________
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                            Last edited by DYasny; 6th March 2011, 18:25.
                            Real stupidity always beats Artificial Intelligence (c) Terry Pratchett

                            BA (BM), RHCE, MCSE, DCSE, Linux+, Network+

                            Comment


                            • #15
                              Re: How many virtual machines

                              Results of my test.

                              I spread 6 VM's to my 3 hard disks (2 VM's per), with the result that I am now running 6 virtual machines with no perceptible decrease in responsiveness.

                              Jas:
                              It appears to me that you hit the nail on the head with your comment that I was "burying the needle on disk I/O".

                              Thanks

                              a

                              ps; more stupid questions to come.

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