6.5.1

Host Configuration
Hosts running the Primary and Secondary VMs should operate at approximately the same processor
frequencies, otherwise the Secondary VM might be restarted more frequently. Platform power management
features that do not adjust based on workload (for example, power capping and enforced low frequency
modes to save power) can cause processor frequencies to vary greatly. If Secondary VMs are being restarted
on a regular basis, disable all power management modes on the hosts running fault tolerant virtual
machines or ensure that all hosts are running in the same power management modes.
Host Networking Configuration
The following guidelines allow you to congure your host's networking to support Fault Tolerance with
dierent combinations of trac types (for example, NFS) and numbers of physical NICs.
n
Distribute each NIC team over two physical switches ensuring L2 domain continuity for each VLAN
between the two physical switches.
n
Use deterministic teaming policies to ensure particular trac types have an anity to a particular NIC
(active/standby) or set of NICs (for example, originating virtual port-id).
n
Where active/standby policies are used, pair trac types to minimize impact in a failover situation
where both trac types will share a vmnic.
n
Where active/standby policies are used, congure all the active adapters for a particular trac type (for
example, FT Logging) to the same physical switch. This minimizes the number of network hops and
lessens the possibility of oversubscribing the switch to switch links.
N FT logging trac between Primary and Secondary VMs is unencrypted and contains guest network
and storage I/O data, as well as the memory contents of the guest operating system. This trac can include
sensitive data such as passwords in plaintext. To avoid such data being divulged, ensure that this network is
secured, especially to avoid 'man-in-the-middle' aacks. For example, you could use a private network for
FT logging trac.
Homogeneous Clusters
vSphere Fault Tolerance can function in clusters with nonuniform hosts, but it works best in clusters with
compatible nodes. When constructing your cluster, all hosts should have the following conguration:
n
Common access to datastores used by the virtual machines.
n
The same virtual machine network conguration.
n
The same BIOS seings (power management and hyperthreading) for all hosts.
Run Check Compliance to identify incompatibilities and to correct them.
Performance
To increase the bandwidth available for the logging trac between Primary and Secondary VMs use a
10Gbit NIC, and enable the use of jumbo frames.
You can select multiple NICs for the FT logging network. By selecting multiple NICs, you can take
advantage of the bandwidth from multiple NICs even if all of the NICs are not dedicated to running FT.
Store ISOs on Shared Storage for Continuous Access
Store ISOs that are accessed by virtual machines with Fault Tolerance enabled on shared storage that is
accessible to both instances of the fault tolerant virtual machine. If you use this conguration, the CD-ROM
in the virtual machine continues operating normally, even when a failover occurs.
vSphere Availability
52 VMware, Inc.