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Performance Tuning for Backups

You can create additional settings to control VM dispatching, volume activity, stream allocation, and transport modes.

For an overview of the default behavior, see one of the following topics on VM Dispatch, Throttling, and Load Balancing:

VM Dispatch

Adjustment Configuration Notes
Disable dynamic VM assignment and force static assignment. Create the bDynamicVMAssignmentAllowed additional setting on the coordinator (and failover candidates) and set the value to false When dynamic VM assignment is disabled, virtual machines are assigned to proxies at the beginning of the job and assignments are not modified during the course of the job.

If this additional setting is configured with a value of true, dynamic VM assignment is allowed but is not forced.

Disable static VM assignment and force dynamic assignment. Create the bStaticVMAssignmentAllowed additional setting on the coordinator (and failover candidates) and set the value to false. Disabling static assignment enables VMs to be assigned on request from the proxy, instead of assigning all static VMs at the beginning of a backup job.

If this additional setting is configured with a value of true, static VM assignment is allowed but is not forced.

(Hyper-V only) Disable VM dispatch to CSV owner. Create the bEnableCSVOwnerDispatch additional setting on the VSA proxy and set the value to false. By default, virtual machines are dispatched to the agent on the host that owns the cluster shared volume (CSV) that the VM is stored on.

Proxy Selection

Adjustment Configuration Notes
(VMware and Hyper-V only) Distribute virtual machine backups across available proxies without priority for proxies on the same host. Create the bEnableHostDispatch additional setting on the VSA proxy and set the value to 0. By default, virtual machines are backed up by proxies running as virtual machines on the same host (highest priority).
(VMware only) Distribute virtual machine backups across available proxies without priority for proxies on hosts that have access to the datastore. Create the bEnableDatastoreDispatch additional setting on the VSA proxy and set the value to 0. By default, virtual machines are backed up by proxies running as virtual machines on hosts that have access to the datastore (second priority).
Distribute virtual machine backups across available proxies without priority for proxies on the same subnet as the VM host. Create the bEnableSubnetDispatch additional setting on the VSA proxy and set the value to 0. By default, virtual machines are backed up by proxies that are on the same subnet as the virtual machine’s host (third priority).
(Hyper-V) Use the coordinator node for all backups. Create the bEnableFailoverOnlyDispatch additional setting on the VSA proxy and set the value to 1. By default, virtual machine backups are distributed to all available VSA proxies for load balancing and failover. This key enables non-coordinator proxies to be used only for failover. All VMs are dispatched to the coordinator node and additional nodes remain idle during the backup.

Datastore Throttling

Adjustment Configuration Notes
(VMware only) Limit the number of VMs from the same datastore that can be backed up at the same time. Create the nVolumeActivityLimit additional setting on the coordinator (and failover candidates) to specify the maximum number of VMs from the same datastore that can be backed up at the same time. When this setting is used and the limit for a datastore is reached, the coordinator stops distributing VMs from that datastore until the backup for another VM on the datastore is complete.

Stream Allocation

Adjustment Configuration Notes
Limit the total number of streams that can be assigned to a proxy when other proxies are competing for streams. Create the nStreamLimit additional setting on the VSA proxy and specify the total number of streams. If this additional setting is configured, the stream limit specified in the additional setting overrides the stream limit based on the proxy's resources that is calculated by the coordinator.

This setting does not prevent additional streams from being assigned to the proxy if all other proxies are at their stream limit.  To prevent streams from being assigned to a proxy that is at the specified stream limit, also add the bHardStreamLimit setting.

Limit the number of streams per CPU that can be assigned to a proxy. Create the nStreamsPerCPU additional setting on the VSA proxy and specify the number of streams per CPU. By default, 10 streams can be assigned for each CPU on the proxy.
Specify the number of MBs of memory that is needed to support a single stream in a proxy.  Create the nMemoryMBPerStream additional setting on the VSA proxy and specify the number of MBs. By default, 1 stream can be assigned for each 100 MBs of memory in the proxy.
Pause stream distribution when all proxies are at their resource limits. Create the bHardStreamLimit additional setting on the coordinator (and failover candidates) and set the value to true If all proxies are at their stream limit, a new backup job that is unable to obtain a stream goes to pending.

Transport Mode

Adjustment Configuration Notes
(VMware only) Disable SAN mode backup. Create the bEnableSanDatastoreDispatch additional setting on the coordinator (and failover candidates) with the value false. Controls whether virtual machine backups are dispatched to VSA proxies based on each proxy's access to the virtual machine's primary datastore.