25. VAAI

VMware’s vStorage APIs for Array Integration, or VAAI, allows storage tasks such as large data moves to be offloaded from the virtualization hardware to the storage array. These operations are performed locally on the NAS without transferring bulk data over the network.

25.1. VAAI for iSCSI

VAAI for iSCSI supports these operations:

  • Atomic Test and Set (ATS) allows multiple initiators to synchronize LUN access in a fine-grained manner rather than locking the whole LUN and preventing other hosts from accessing the same LUN simultaneously.
  • Clone Blocks (XCOPY) copies disk blocks on the NAS. Copies occur locally rather than over the network. The operation is similar to Microsoft ODX.
  • LUN Reporting allows a hypervisor to query the NAS to determine whether a LUN is using thin provisioning.
  • Stun pauses virtual machines when a pool runs out of space. The space issue can then be fixed and the virtual machines can continue rather than reporting write errors.
  • Threshold Warning the system reports a warning when a configurable capacity is reached. In FreeNAS®, this threshold is configured at the pool level when using zvols (see Table 11.5.1) or at the extent level (see Table 11.5.6) for both file and device based extents. Typically, the warning is set at the pool level, unless file extents are used, in which case it must be set at the extent level.
  • Unmap informs FreeNAS® that the space occupied by deleted files should be freed. Without unmap, the NAS is unaware of freed space created when the initiator deletes files. For this feature to work, the initiator must support the unmap command.
  • Zero Blocks or Write Same zeros out disk regions. When allocating virtual machines with thick provisioning, the zero write is done locally, rather than over the network. This makes virtual machine creation and any other zeroing of disk regions much quicker.