We have several options to load balance target devices to vDisks. Under Subnet Affinity, they are None, Best Effort and Fixed.

If we want to restrict PVS vDisk streaming to only some subnets, where PVS servers are spread across different subnets, we can use subnet affinity feature.

Subnet Affinity

When assigning the server and NIC combination to provide a vDisk to target devices, select from the following subnet settings:

None:

• Ignore subnets; use least busy server.
• None is the default setting.

Best Effort:

• Use the least busy server/NIC combination from within the same subnet.
• If no server/NIC combination is available within the subnet, select the least busy server from outside the subnet.
• If more than one server is available within the selected subnet, perform load balancing between those servers.

Fixed:

• Use the least busy server/NIC combination from within the same subnet.
• Perform load balancing between servers within that subnet.
• If no server/NIC combination exists in the same subnet, do not start target devices assigned to this vDisk.

Auto Rebalance

Rebalance enabled using Trigger Percent:

• Enable to rebalance the number of target devices on each server in the event that the trigger percent is exceeded.
• When enabled, PVS checks the trigger percent on each server approximately every ten minutes. For example, if the trigger percent on this vDisk is set to 25%, rebalancing occurs within ten minutes if this server has 25% more load in comparison to other servers that can provide this vDisk.
• This is based on the number of targets currently connected to the server using the specified vDisk.

Note: The load balance algorithm takes into account the PVS Properties of each server when determining the load.

Load balancing will not occur if:

• Less than five target devices are using a particular server.
• The average number of target devices using all qualifying servers is less than five.
• The number of target devices that are starting on a given server is more than 20% of the total number of devices connected to the server (preventing load shift thrashing during a ‘boot storm’).

Load balancing is considered when target devices start. PVS determines the qualified PVS Server with the least amount of load and provides the vDisk. When a qualified server is brought online, rebalancing will occur automatically.

Note: Enabling both Subnet Affinity and Auto Rebalance might cause a reconnect storm to occur. This could cause the stream process on the PVS server to fail and target devices to become unresponsive.

Citrix does not recommend enabling both features.