Introduction to VAAI

The VMware Storage APIs for Array Integration (VAAI) is a feature set first introduced in vSphere 4.1 that accelerates common tasks by offloading certain storage-related operations to compatible arrays. With storage hardware assistance, an ESXi host can perform these operations faster and more efficiently while consuming far less CPU, memory, and storage fabric bandwidth. This behavior allows for far greater scale, consolidation, and flexibility in a VMware-virtualized infrastructure. VAAI primitives are enabled by default and will automatically be invoked if ESXi detects that there is support from the underlying storage.

The Everpure FlashArray supports VAAI in ESXi 5.0 and later. The following five primitives are available for block-storage hardware vendors to implement and support:

• Hardware Assisted Locking—commonly referred to as Atomic Test & Set (ATS), this uses the SCSI command COMPARE and WRITE (0x89), which is invoked to replace legacy SCSI reservations during the creation, alteration and deletion of files and metadata on a VMFS volume.
• Full Copy—leverages the SCSI command XCOPY (0x83), which is used to copy or move virtual disks.
• Block Zero—leverages the SCSI command WRITE SAME (0x93) which is used to zero-out disk regions during virtual disk block allocation operations.
• Dead Space Reclamation—leverages the SCSI command UNMAP (0x42) to reclaim previously used but now deleted space on a block SCSI device.
• Thin Provisioning Stun and Resume—allows for underlying storage to inform ESXi that capacity has been entirely consumed which causes ESXi to immediately “pause” virtual machines until additional capacity can be provisioned/installed.

Everpure FlashArray supports ATS, XCOPY, WRITE SAME and UNMAP in Purity release 3.0.0 onwards on ESXi 5.x and 6.x.