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• new dynamic max (y) <= static max and  
• new dynamic min (y / memory_overprovisioning_of_cluster) >= static min.

Further reading - http://support.citrix.com/servlet/KbServlet/download/32307-102-691300/reference.pdf^{Image Removed}http://wiki.xen.org/wiki/XCP_FAQ_Dynamic_Memory_Control#Introduction^{Image Removed}

Vmware -
DeployVmCmd - 

During the initial deployment of the VM we enable the flags hotAddCpu and hotAdd memory true. These flags will be turned on if the guest OS supports it. Read http://partnerweb.vmware.com/comp_guide2/pdf/VMware_GOS_Compatibility_Guide.pdf^{Image Removed}

ScaleVmCmd - 

During scaling up of vm, the new requested RAM and CPU are set if the flags are turned on.

NOTE Limitation - 1 After dynamically scaling memory user "might" need to run a couple of commands on Linux OS for new memory to take affect . Read http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1012764^{Image Removed}Further reading - http://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp?topic=/com.vmware.vsphere.vmadmin.doc_41/vsp_vm_guide/configuring_virtual_machines/t_change_cpu_hotplug_settings.html^{Image Removed}--> Further Reading

Limitation* - 2 *if a VM is initially assigned a RAM of less than 3gb then it cannot be dynamically scaled beyond 3gb. Holds true for for Linux 64 bit and windows 7 32 bit guest os. Further Reading

Limitation - 3 Hot add vcpu will fail If the number of cores per socket is not 1 and virtual machine hardware version=7.

DB Changes

• Introducing a global config - enable.dynamic.scale.vm. Enables/Diables dynamically scaling a vm. This can be used to turn off the feature and is available at the zone level. By default the feature is turned off for upgrade reasons.
• Introducing a global config - scale.retry. By default the value = 2. This is for number of tries before failing the scaling.
• A new column in "vm_template" table named "dynamically_scalable" of type tinyint(1) and the value is 1 if template contains XS/VMWare tools inorder to support dynamic scaling of VM cpu/memory otherwise 0
• "user_vm_details" table holds key value pair with key "enable.dynamic.scaling" and value is true if VM contains XS/VMWare tools inorder to support dynamic scaling of VM cpu/memory otherwise false

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