Dell Storage with Microsoft Storage Spaces Best Practices Guide

When Dynamic Memory is enabled during VM configuration, Dell recommends that the sum of the maximum RAM setting for all VMs not exceed the physical memory capacity of the compute cluster, as calculated in the previous section.

Enabling Dynamic Memory will intermittently add a small latency for each reallocation of memory and add some overhead in the host OS related to memory management in the virtualized environment.

Following is a summary of VM settings related to Dynamic Memory. These settings can be configured using the Set-VM PowerShell cmdlet or using the Hyper-V Manager and must be configured on the node where the VM resides.

Startup RAM

The startup RAM value can be set when creating a VM using the New-VM and the Set-VM cmdlets or it can be set by using the Hyper-V manager for the VM, under the hardware settings for memory.

The Startup RAM value specifies the amount of memory required when a VM is powered on. This value can exceed the minimal RAM level when the memory required to start a guest OS is more than the minimum amount needed to run the guest OS.

Minimum RAM

Specifies the minimum amount of memory to allocate to the VM after the VM has started. Valid values range from 32 MB to the default value, which is the Startup RAM.

Maximum RAM

Sets Maximum RAM that can be assigned to the VM. It is important to set this to a reasonable value on all VMs to prevent a single VM, in error, starving the other VMs. When Dynamic Memory is enabled, its default maximum is 1 TB, which is too high. Be aware that this value can be increased anytime, but to reduce the value, the VM must be turned off.

Memory Buffer

Percentage to reserve as a buffer over current demand to ensure quick response to changes in memory usage by the VM to minimize repeated reallocations of memory.

Memory weight

Sets priority for VM for memory resources compared to other VMs in the situation where there is not sufficient available memory to give every VM its requested amount of memory.