1. Processor Requirements
Any host used for Lync virtual machines should have a modern
processor, which is 2.26 GHz or faster. This means that the CPU used
should be manufactured at least from January of 2009 or later to
achieve the required performance. From a planning perspective, the
number of logical cores on the processor determines the maximum number
of virtual machines that can run on the host. To fall within the Lync
support boundaries, each virtual machine must have four dedicated CPU
cores. This means that for a server that has eight cores, only two Lync
virtual machines can run on the host, whereas a server with 16 cores
can support up to four Lync virtual machines.
Note
The host server is not going to consume many
CPU cycles, so for planning purposes it is acceptable to ignore trying
to dedicate a core to the host. If cores for the host were included,
everyone would wind up with an odd number of CPU cores.
The number of cores is the important value here, not the
number of physical processors. For example, two quad-core processors
are equivalent to four dual-core processors. Both yield eight physical
cores that can be used by virtual machines.
2. Memory Requirements
To meet the support requirements, each Lync Server virtual machine
must be allocated a minimum of 15 GB of RAM. This memory should be
allocated exclusively for each virtual machine. Hyper-V Service Pack 1
has a new feature called Dynamic Memory that allows defining startup
and maximum RAM values for a virtual machine. This feature should not
be used with Lync Server 2010, or if it is, the startup RAM for each VM
should be at least 15 GB to guarantee that amount is always available.
Likewise, virtual machines that run on VMware should not be
overcommitted on memory. VMware allows administrators to collectively
assign more memory to virtual machines than is actually physically
installed in the host server. This feature cannot be used with Lync and
will have a negative impact on performance.
Note
When planning for memory allocation, it is
important to reserve some memory for the host operating system. This
amount varies based on the hypervisor and can be anywhere from 512 MB
to 2 GB. It seems the Lync Server team is already planning for this by
defining a minimum of 15 GB for virtual machines where the physical
counterparts require at least 16 GB. The extra 1 GB leaves some memory
for the host. As more virtual machines are placed on the host, more
memory can be made available to the host server.
3. Disk Requirements
The only support requirement dictated by Microsoft around disk space
is that each host must support at least 500 GB of free space. The
actual space consumed by Lync virtual machines varies by role and by
business requirements for monitoring or archiving data. Using fixed or
dynamically expanding disks also has a big effect on how much space is
required. Generally, allocating 40 to 50 GB of disk space per virtual
machine for the operating system is sufficient. Lync Back-End database
Servers or Monitoring and Archiving Servers with a collocated SQL
database are going to consume much more space than a Front-End or Edge
Server.
Both direct attached storage (DAS) and SAN disks are supported to
hold Lync virtual machines. Which option is used depends greatly on the
infrastructure that an organization already has in place. SAN
provisioning is generally more flexible, but there is a significant
upfront cost to these types of systems. DAS storage can be more
affordable and yield acceptable performance for virtual machines.
Another consideration for organizations is whether to use a single
RAID volume for all virtual machines or to separate each virtual
machine disk on to its own physical hard disk. There is no requirement
for separate disk spindles, but the best performance is realized if
each virtual machine disk can be placed on a dedicated hard disk
spindle. The downside to dedicated disks is that unless the disk count
is doubled, there is no redundancy at the physical disk level. Many
organizations find that placing virtual hard disks on a RAID 1+0 or
RAID 5 volume meets the disk requirements of most virtual machines.
Note
Separating the disks used for the host system
shows a performance benefit both for the host and guest VMs. A common
configuration for host machines is to use two hard disks in a RAID 1
mirror set for redundancy, and then provision the remaining number of
disks in a RAID 1+0 or RAID 5 configuration for virtual machine
storage. This way, the host reads and writes do not compete with the
virtual machine hard disk activity.
4. Networking Requirements
A fairy strict suggestion from Microsoft around network adapters is
that a dedicated network adapter should be used for each Lync virtual
machine. In a traditional virtualization environment, most virtual
machines share traffic through a single or teamed set of physical
network adapters. Virtual machines compete for network bandwidth
resources through the same physical links and can be subject to delays
or queues when other virtual machines have heavy bursts of traffic.
Caution
To avoid Lync Servers being affected
by these contention issues, Microsoft recommends providing a dedicated
physical adapter for each Lync virtual machine. This ensures that each
Lync Server has a direct connection to a switch that can help eliminate
jitter or delay problems encountered when sharing adapters.
5. Operating System Requirements
As indicated previously, the only supported hypervisors today are
Microsoft Windows Server 2008 R2 Hyper-V and VMware vSphere 4. More
hypervisor support might become available at a later time as vendors
certify a platform with Microsoft. For Microsoft, either the full or
core installation of Windows Server 2008 R2 can be used. The
standalone, free product Microsoft Hyper-V R2 can also be used to
virtualize Lync Servers. On the VMware side, both the ESX and ESXi
platforms can be used.
6. Software Recommendations
In addition to the support requirements, there are some general
recommendations that can help improve the performance of the Lync
virtual servers. The first is to use host servers only for
virtualization. Do not run additional applications or services on
servers that host virtual machines. These applications or services have
processing, memory, and network requirements that might have an adverse
effect on virtual machines.
The second recommendation is to properly configure any
anti-virus application because anti-virus applications that run on a
host server can have a serious performance effect on virtual machines.
Any locations with a virtual disk file should be excluded from virus
scans to avoid performance issues. Anti-virus applications are not
aware of how to scan a virtual disk file, so they treat it as any other
file. Because virtual disk files are quite large, this can cause
performance issues while the anti-virus application attempts to scan
the file.
