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Improving VMware VAAI performance for ESX hosts

ONTAP supports certain VMware vStorage APIs for Array Integration (VAAI) features when the ESX host is running ESX 6.0U3 or later. These features help offload operations from the ESX host to the storage system and increase the network throughput. The ESX host enables the features automatically in the correct environment.

The VAAI feature supports the following SCSI commands:

  • EXTENDED_COPY
    This feature enables the host to initiate the transfer of data between the LUNs or within a LUN without involving the host in the data transfer. This results in saving ESX CPU cycles and increasing the network throughput. The extended copy feature, also known as "copy offload," is used in scenarios such as cloning a virtual machine. When invoked by the ESX host, the copy offload feature copies the data within the storage system rather than going through the host network. Copy offload transfers data in the following ways:
    • Within a LUN
    • Between LUNs within a volume
    • Between LUNs on different volumes within a storage virtual machine (SVM)
    • Between LUNs on different SVMs within a cluster
    If this feature cannot be invoked, the ESX host automatically uses the standard READ and WRITE commands for the copy operation.
  • WRITE_SAME

    This feature offloads the work of writing a repeated pattern, such as all zeros, to a storage array. The ESX host uses this feature in operations such as zero-filling a file.

  • COMPARE_AND_WRITE

    This feature bypasses certain file access concurrency limits, which speeds up operations such as booting up virtual machines.