Optimizing the Cloud: Nova/KVM

Sources:[“ http://www.slideshare.net/openstackindia/openstack-nova-and-kvm-optimisation”,” http://www.linux-kvm.org/page/KSM”,” http://pic.dhe.ibm.com/infocenter/lnxinfo/v3r0m0/index.jsp?topic=%2Fliaat%2Fliaattunkickoff.htm”]

Compute nodes represent a potential bottleneck in an OpenStack Cloud Environment, because the compute nodes run the VM’s and Applications, the workloads fall on the I/O within the Hypervisor. Everything from Local File system I/O, RAM Resources and CPU can all affect the efficiency of your cloud.

One thing to consider when provisioning physical machines is to look at what Guest/VM flavours you are going to allow to be deployed on that machine. Flavours that eat up 2VCPUs and 32G of RAM may not be well suited with a machine with only 64G of RAM and 8 CPU Cores

The notion of tenancy is also important to keep track of, tenant size and activity factors into how your environments resources are used. Tenants consume images, snapshots, volumes and disk space. Consider how many tenants will consume your cloud and adjust your resources accordingly. Make sure if you plan to take advantage of overprovisioning think about thin provisioning and potential performance hits.

Using KVM:

KVM is a well-supported hypervisor for Nova and has its own ways to increase performance. KVM isn’t the only Hypervisor to choose, Hyper-V, Xen, VMware can also be supported in Openstack, but KVM is a powerful competitor. Tuning your hypervisor is just as important as tuning your cloud resources and environment, so here are some things to consider:

  • I/O Scheduler: cfq vs deadline
  • Huge Pages
  • KSM (Kernel Same-page Merging)
    • A de-duplication feature, saves on memory usage. Helps scale vms/per hypervisor node (compute node)
  • Hyper-threading
  • Guest FS location (on hypervisor block devices)
  • Disable Zone Reclaim
  • Swappiness

Personally running Grizzly, we can see that KSM is working,

cat /sys/kernel/mm/ksm/pages_sharing

1099262

Running Ubuntu linux 3.2.00-23 kernel ns qemu-kvm-1.0. This should mean that running multiple VM’s should have better performance.

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