Creating and Configuring Storage Devices - Mastering VMware vSphere 5.5 - page 320

T10 committee in charge of the SCSI standards, it does require appropriate support from stor-
age vendors, so you'll want to check with your storage vendor to see what is required in order to
support VAAI. In addition to the VAAI features introduced in vSphere 4.1 and 5.0, vSphere 5.5
introduces even more storage ofl oads. Here's a quick rundown of the storage ofl oads available
in vSphere 5.5:
Hardware-Assisted Locking Also called atomic test and set (ATS), this feature supports
discrete VM locking without the use of LUN level SCSI reservations. In the section titled
“Examining the vSphere Virtual Machine File System,” we briel y described how vSphere
uses SCSI reservations when VMFS metadata needs to be updated. Hardware-assisted lock-
ing allows for disk locking per sector instead of locking the entire LUN. This offers a dra-
matic increase in performance when lots of metadata updates are necessary (such as when
powering on many VMs at the same time).
Hardware-Accelerated Full Copy Support for hardware-accelerated full copy allows stor-
age arrays to make full copies of data completely internal to the array instead of requiring the
ESXi host to read and write the data. This causes a signii cant reduction in the storage trafi c
between the host and the array and can reduce the time required to perform operations like
cloning VMs or deploying new VMs from templates.
Hardware-Accelerated Block Zeroing Sometimes called write same, this functionality
allows storage arrays to zero out large numbers of blocks to provide newly allocated storage
without any previously written data. This can speed up operations like creating VMs and
formatting virtual disks.
Thin Provisioning vSphere 5.0 added an additional set of hardware ofl oads around thin
provisioning. First, vSphere is thin-provisioning aware, meaning that it will recognize
when a LUN presented by an array is thin provisioned. In addition, vSphere 5.0 added and
vSphere 5.5 improves on the ability to reclaim dead space (space no longer used) via the
T10 UNMAP command; this will help keep space utilization in thin-provisioned environ-
ments in check. Finally, vSphere also has support for providing advance warning of thin-
provisioned out-of-space conditions and provides better handling for true out-of-space
conditions.
Standards-Based or Proprietary?
So is the functionality of VAAI standards based or proprietary? Well, the answer is a little of
both. In vSphere 4.1, the hardware-accelerated block zeroing was fully T10 compliant, but the
hardware-assisted locking and hardware-accelerated full copy were not fully T10 compliant and
required specifi c support from the array vendors. In vSphere 5.5, all three of these features are
fully T10 compliant, as is the thin-provisioning support, and will work with any array that is also
T10 compliant.
h e NAS o oads, however, are not standards based, and will require specifi c plug-ins from the
NAS vendors to take advantage of these o oads.
Like previous versions, vSphere 5.5 includes hardware ofl oads for NAS:
Reserve Space This functionality lets you create thick-provisioned VMDKs on NFS data-
stores, much like what is possible on VMFS datastores.