
// Module included in the following assemblies:
//
// * virt/live_migration/virt-about-live-migration.adoc

:_mod-docs-content-type: CONCEPT
[id="virt-vm-migration-tuning_{context}"]
= VM migration tuning

[role="_abstract"]
You can adjust your cluster-wide live migration settings based on the type of workload and migration scenario.

This enables you to control how many VMs migrate at the same time, the network bandwidth you want to use for each migration, and how long {VirtProductName} attempts to complete the migration before canceling the process. Configure these settings in the `HyperConverged` custom resource (CR).

If you are migrating multiple VMs per node at the same time, set a `bandwidthPerMigration` limit to prevent a large or busy VM from using a large portion of the node's network bandwidth. By default, the `bandwidthPerMigration` value is `0`, which means unlimited.

A large VM running a heavy workload (for example, database processing), with higher memory dirty rates, requires a higher bandwidth to complete the migration.

[NOTE]
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Post copy mode, when enabled, triggers if the initial pre-copy phase does not complete within the defined timeout. During post copy, the VM CPUs pause on the source host while transferring the minimum required memory pages. Then the VM CPUs activate on the destination host, and the remaining memory pages transfer into the destination node at runtime. This can impact performance during the transfer.

Post copy mode should not be used for critical data, or with unstable networks.
====
