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What operations do VMware vStorage APIs accelerate?

VMware's vStorage APIs for Array Integration functionality enables storage devices that support VAII to reduce traffic on the network and reduce some work on the server to speed up input/output tasks.

Every time read or write file access takes place, software at the operating system and system BIOS uses local memory cache and CPU interrupts to move data blocks across the storage fabric or enterprise LAN. This kind of traditional storage activity can bog down enterprise servers and storage networks busy with storage-intensive tasks.

But a new generation of storage hardware includes acceleration features that can conduct certain functions directly within the storage array without the need to generate routine network traffic -- saving system CPU, memory and bandwidth. VMware ESXi supports hardware acceleration with suitable storage subsystems.

VMware uses vStorage APIs for Array Integration (VAAI) to provide support for five general operations; copying, zeroing, locking, provisioning and deleting. Let's look at the effects and benefits of each operation.

Copying features include cloning blocks, full copies and extended copy, or XCopy, capabilities used to copy data or migrate VM files within the same storage array. This means a server does not need to read data from the storage array first and then resend the same data to a new place on the array. VM cloning or vMotion tasks can be vastly accelerated.

Zeroing can zero blocks or write same -- duplicate the same block -- to initialize disk regions on the array. This avoids having to use a server to send a continuous stream of zeros to a newly provisioned LUN, so new LUN creation and VM deployment are considerably faster.

Locking is handled by Atomic Test and Set, or ATS, features, which control the way that a LUN is protected. Rather than locking or unlocking an entire LUN, blocks within the LUN can be locked or unlocked -- for a more granular or "atomic" approach -- which allows other VMs to continue sharing unlocked areas of the LUN and causing less disruption with other servers or workloads sharing the LUN.

Finally, recovering unused or unneeded space can be a challenge, and VAAI functions provide space reclamation capabilities used with thin provisioning and direct-block deletion. This improves storage management and reduces waste, which saves on storage capital expenditures.

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