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VMWARE B E S T P R A C T I C E S
In order to ensure that you meet your organization’s availability
targets, consider providing the following for your ESX Server
hosts:
• Redundant HBAs — Do not use a single dual-port card. A
minimum of two cards is required for redundancy.
• Redundant power supplies.
• Redundant network connections to each required VLAN.
Consider port trunking if many VLANs must be supported.
• Mirrored ESX Server operating system drives.
• Redundant core network switches with the redundant
network adapters connected to separate switches.
• Redundant SAN switches with HBA connections to separate
switches.
If you do not have redundancy in your current configuration,
and it is not within your budget, do the best you can, but com-
municate the risks to your organization
Virtual Machine Mobility
In addition to configuring ESX Server hosts to allow VMotion
of virtual machines among the hosts, you should deploy the
hosts in clusters in which all hosts are similarly configured so
Exchange-related virtual machines can run equally well on any
host. By enabling virtual machine mobility through VMotion,
you give your solution the following benefits:
• VMware DRS (Distributed Resource Scheduler) and VMware
HA – VMware DRS tracks the performance of virtual machines
and, depending on configuration, recommends target hosts
for best performance or actually migrates hosts based on
policy. VMware HA automatically restarts virtual machines
that run on hosts that experience a failure — for example, if a
motherboard fails or the host panics.
• You can perform hardware maintenance without affecting
availability. You can migrate virtual machines to other hosts
before maintenance, then migrate them back after you finish
the maintenance.
• You can allocate resources in advance for planned peaks. If
you know that a virtual machine will require more processor
resources for a process that occurs at the end of the week,
such as database maintenance, you can migrate that virtual
machine to an underutilized host for that period of time.
This allows you to maintain service levels during the task.
When the peak need has passed, you can migrate the virtual
machine back to its normal host. You can even script and
schedule this process.
• You can migrate virtual machines to a host you are not using
or to an underutilized host for troubleshooting. This allows
you to isolate a virtual machine that is experiencing an appli-
cation issue.
Hardware Resources
The overall capacity of your hosts must be great enough to
provide resources for all of the virtual machines you plan to run
there and must provide room for the variability of the overall
system. In RapidApp’s practice, most of our designs — which
are all determined by our clients with direction from our archi-
tects — have used a major brand of four-processor host with
from 24GB to 48GB of RAM. The amount of RAM is determined
by the expected average RAM per virtual machine multiplied
by the expected number of virtual machines per host. RAM
and processor have typically been the bottleneck for the imple-
mentations we have performed. For example, if you are using
new dual-core processors and expect to support 25–32 virtual
machines per host with each virtual machine using between
1GB and 1.5GB of RAM, you would design for (16 × 1) + (16 ×
1.5) or 40GB of RAM. You could choose to round up to 48GB, or
you might want to reduce the cost and use 32GB. Although the
latter choice limits the number of virtual machines on the host,
you might determine that it is better to spend the saved money
on another server.
ESX Server 3 has the ability to run virtual machines with up
to four virtual processors. Exchange is multithreaded, and can
often take advantage of two processors. However, in order to
avoid performance penalties due to scheduling conflicts, it is
recommended that the number of physical processors exceed
the maximum number of virtual processors on a single virtual
machine. Therefore, if you intend to use two-way Virtual SMP
virtual machines for Exchange, you should plan for servers with
at least four processor cores.
In contrast to CPU and memory, network and HBA configu-
rations are usually governed by security and redundancy
concerns rather than capacity. In our analysis, network
bandwidth is not a significant factor in Exchange Server per-
formance, since in most large-scale deployments, hosts are
provided gigabit connectivity
You must provide adequate excess capacity within a cluster.
The system should be able to handle a server failure with no
performance degradation. If it takes a long time in your orga-
nization to have hardware repaired, you should provision still
more capacity. Remember: since significant savings result from
deploying virtualization in the first place, this is not the place to
cut corners.
Quality of Hardware
Use quality servers and components in your design. Again, you
achieve substantial reductions in the number of physical servers
deployed in the environment, so don’t settle for lesser quality
server hardware and SAN infrastructure components. Ensure
that all hardware is on the VMware hardware compatibility
list and that the hardware meets your other criteria for perfor-
mance, scalability, and availability.
