1. Processor Requirements
All virtual machines that run a Lync Server 2010 role must
have four virtual processors assigned. This is because processing media
requires many CPU cycles, so Microsoft recommends dedicating logical
cores to each virtual machine.
2. Memory Requirements
Each virtual machine that runs a Lync Server 2010 role must
have at least 15 GB of memory allocated. This value might increase over
time, or it might be necessary to allocate more memory immediately for
a large Back-End database server. 15 GB is the supported minimum tested
by Microsoft, but services can operate with less memory for smaller
environments at the risk of falling outside the support boundary.
3. Disk Requirements
There are no specific disk requirements for virtual machine disks
used with Lync Server 2010. The only consideration is to allocate
enough space for the operating system installation and Lync application
installation. For Back-End database servers, the same planning figures
apply for database sizing. This also applies to the Monitoring and
Archiving database size planning figures.
Disk Types
When creating a virtual machine, options exist to create a hard disk
for the VM as a fixed size or dynamically expanding. In VMware, the
dynamically expanding disk is referred to as thin provisioning.
The difference is that with a fixed-size disk, the space allocated to a
virtual machine is immediately accounted for on the host operating
system disk volume. For instance, if the host has 500 GB of free disk
space and a 100 GB fixed size disk is created, the host will reflect
400 GB of free space. Dynamically expanding disks differ in that a
maximum size is specified that the disk can grow to, but the space is
not immediately consumed. Continuing the previous example, the virtual
machine still believes it has a 100 GB hard disk, but space on the host
physical disk is consumed only as the virtual machine begins to write
data to the disk. The virtual disk is negligible at first, but it might
consume 10 GB of space after an operating system is installed, and more
when applications and data are added.
Caution
The advantage, and danger, to dynamically
expanding disks is that disk space can be over-allocated. Virtual
machines appear to have more disk space available to them than might be
actually present on the disk, but this allows organizations to
provision more virtual machines because they might not require that
much space.
A third type of option in disk configuration for virtual machines is
to use pass-through disks. Pass-through disks present a physical hard
disk directly to a virtual machine. This configuration is not as
typical for small environments, but where performance must be
guaranteed, and resources not shared with other virtual machines,
pass-through disks are an attractive option.
In earlier versions of virtualization products, the rule of thumb
was that fixed-size disks yielded significantly greater performance for
a virtual machine. With the most recent releases from both Microsoft
and VMware, this notion has shifted quite a bit and dynamically
expanding disks are now nearly equal in performance after they have
been initially expanded. This means that the first time an application
writes to a virtual disk, a fixed-size disk will be quicker because a
dynamically expanding disk has to first grow the disk before writing
the data. At the point where the dynamically expanding disk no longer
is growing in size though, the performance is nearly equal.
For SQL Servers, the Microsoft SQL Server team recommends using
either fixed-size disks or pass-through disks, so it might make sense
to use these types for a Back-End Server.
Note
For the other roles in Lync Server, it
becomes a business or policy decision to use dynamically expanding
disks. Initial performance might not be as good, but when the disks
reach a growth plateau, the performance is on par with fixed-size disks
and uses significantly less disk space.
4. Networking Requirements
Each virtual machine running a Lync Server 2010 role should have at
least one virtual network adapter added. Edge Servers require at least
two adapters just as with a physical installation.
Synthetic Device Drivers
Both the Hyper-V and VMware virtualization products contain emulated
and synthetic device drivers. Emulated drivers were the original
approach to virtualization where each hard disk or network adapter
assigned to a virtual machine is emulated in software. The advantage to
emulated drivers is that almost all operating systems contain support
for these drivers because it emulates a baseline set of abilities.
Synthetic drivers are used to provide an additional level of
performance and abilities within a virtual machine such as jumbo frames
or TCP offloading features.
In general, synthetic device drivers cannot be used in a virtual
machine until special software is installed in the guest operating
system to provide these drivers. In Microsoft Hyper-V, these are called
the integration components, whereas in VMware these are referred to as
the VMware tools. In Microsoft Hyper-V, adding a legacy network adapter
device to a virtual machine uses an emulated device driver, but when
adding one of the default network adapters to a virtual machine, the
synthetic device driver is used. For VMware, the VMXNET network adapter
types provide the best performance. With Lync Server 2010, deployments
always use a synthetic network adapter to achieve the best possible
performance.
Virtual Machine Queue
Virtual Machine Queue (VMQ) is a new network adapter feature that
provides some performance benefit in a virtualized environment. VMQ
allows the physical network adapter to provide virtual queues for each
virtual machine running on the host. This allows the hypervisor to pass
external traffic directly to each virtual machine without routing
through the management operating system first. This feature should not
be confused with Virtual Machine Chimney, which is a separate function
that provides TCP offloading features from the guest virtual CPU to the
physical network adapter.
Note
Early versions of driver software that
supported VMQ automatically disabled VMQ if an adapter used for virtual
machines was placed in a network team. If you run an older version of
the driver, be sure to update to the latest release to allow both
teaming and VMQ to function. Support for Hyper-V network adapter
teaming is up to the adapter vendors, so also verify that the hardware
installed is supported by the manufacturer.
If the adapters used on a host machine allow
this feature, it should be enabled for optimal performance in Lync
Server 2010. Because media traffic is extremely sensitive to latency or
delays, any optimizations at the network layer can lead to increased
virtual machine performance. Adapters do not support an unlimited
amount of virtual machine queues, so VMQ should be enabled only for
virtual machines that receive a heavy amount of traffic. VMware
includes a feature called VMDirectPath, which gives a virtual machine direct access to the physical adapters.
Tip
If a physical adapter can be provided for each virtual machine, this feature can be leveraged for increased performance.
Send/Receive Buffers
Microsoft recommends adjusting the send and receive buffers on any
network adapter dedicated to virtual machines to be a value of at least
1024. This helps to improve network performance and reduces the number
of dropped packets.
5. Operating System Requirements
When virtualizing Lync Server 2010, the only supported
guest operating system is Windows Server 2008 R2. Although the original
release of Windows Server 2008 x64 is supported for physical
deployments, it is not supported when deployed within a virtual machine.
6. Software Recommendations
As with a physical host server, the Lync virtual machines
should not run any additional applications or services. Additionally,
any anti-virus applications should be configured to exclude both the
Lync Server 2010 binary files location and the Lync services running.
