Specifications

Best Practices for Virtualizing and Managing Exchange 2013
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Best Practices and Recommendations
Microsoft does not support Dynamic Memory for virtual machines that run any of the
Exchange 2013 roles. Exchange 2013 uses in-memory data caching to provide better
performance and faster I/O operations. To achieve this, Exchange 2013 needs a substantial
amount of memory at all times and full control over the memory. If Exchange 2013 does not have
full control of the memory allocated to the physical or virtual machines on which it is running,
degraded system performance and a poor client experience can result. Therefore, Dynamic
Memory is not supported for Exchange 2013.
Dynamic Memory
While not supported with virtual machines running any Exchange 2013 roles, Dynamic Memory can
still provide a valuable and effective solution for optimizing memory usage for other virtualized
workloads. Virtual machines with Dynamic Memory enabled can coexist without issue on hosts with
other virtual machines that have Dynamic Memory disabled. Earlier versions of Hyper-V only allowed
administrators to assign a fixed amount of physical memory to a virtual machine on the host machine.
Once the memory was assigned, it was not possible to change the memory for that particular virtual
machine during its run state.
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To overcome this problem, Microsoft introduced the concept of Dynamic
Memory in Windows Server 2008 R2 SP1.
With Windows Server 2012, Microsoft has enhanced the Dynamic Memory feature to provide increased
agility around how memory is allocated and managed between virtual machines running on a host.
Dynamic Memory in Windows Server 2012 has introduced two key new enhancements: minimum memory
and Hyper-V smart paging.
Minimum Memory
Minimum memory allows Hyper-V in Windows Server 2012 to reclaim the unused memory from virtual
machines. This results in increased virtual machine consolidation. However, there can be a limitation to
this feature. If you must restart one virtual machine and it has less memory than required for its startup
memory, Hyper-V needs additional memory to restart the machine. Yet, Hyper-V may not always have
additional memory available. Such a situation results in a virtual machine start failure. To overcome this
situation, Dynamic Memory in Windows Server 2012 has introduced Hyper-V Smart Paging.
Hyper-V Smart Paging
Hyper-V Smart Paging is a memory management technique that is used to cover the gap between
minimum memory and startup memory, enabling reliable restart of virtual machines (Figure 28). It uses
disk resources as additional, temporary memory when more physical memory is required to restart a
virtual machine than is currently available.
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