When using VMware vSAN storage and configuring vSphere Replication on multiple virtual machines, the initial full synchronization takes a long time to complete.
Configuring vSphere Replication on a large number of virtual machines simultaneously when using vSphere Replication with vSAN storage causes the initial full synchronization of the virtual machine files to run very slowly.
Initial full synchronization operations generate heavy I/O traffic. Configuring too many replications at the same time can overload the vSAN storage.
Configure vSphere Replication in batches of a maximum of 20 virtual machines at a time.