By default, vSphere provides a mechanism that creates scheduling queues for every virtual machine file. Each file, for example .vmdk, gets its own bandwidth controls.

This mechanism ensures that I/O for a particular virtual machine file goes into its own separate queue and avoids interfering with I/Os from other files.

This capability is enabled by default. You can use the vSphere Client or the esxcli commands to disable or reenable the capability.