vStorage APIs for Array Integration

What Does vStorage APIs for Array Integration Mean?

vStorage APIs for Array Integration (VAAI) is an application program interface (API) framework designed by VMware. VAAI framework lets the ESX/ESXi host offload some storage functions directly to the storage array instead of processing the data on its own.


For example, a standard operation deployment of a virtual machine (VM) from its template demands the ESX/ESXi host read the data from the template by means of the storage protocol in use, then write the data to the storage while cloning the VM. Utilization of VAAI allows these operations to be offloaded to the storage array, reducing the majority of repetitive read-writes. Operations are completed more quickly, resulting in minimal overhead for central processing units (CPU).

Techopedia Explains vStorage APIs for Array Integration

With the introduction of support for block-based storage systems (iSCSI or Fibre Channel) in vSphere 4, the VAAI includes the following parts:

  • Copy offload allows the storage system to make full data copies inside the array, as well as offload that chore from the ESX server.
  • Hardware-aided locking allows vCenter to offload SCSI commands from the ESX server into the storage system. This helps the array potentially manage the locking mechanism when the system carries out data updates.

The thin provisioning improvements from VAAI permit storage arrays that utilize thin provisioning to retrieve blocks of space as soon as a virtual disk is deleted. They also help to offset the possible risk of a thinly provisioned storage array from running out of space.

The thinly provisioned storage systems that support the VAAI of vSphere 5 receive advance warnings once space thresholds are hit. Additionally, VAAI allows mechanisms to pause virtual machines for a specific time period when all available space runs out. This gives admins enough time to add required storage or move the VM to another array.


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Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…