HP 3PAR Solutions Software for vSphere - Manual (Page 12)

2.2 About 3PAR VAAI Plug-in 1.1.0 for VMware vSphere 4.1
3PAR VAAI Plug-in 1.1.0 for VMware vSphere 4.1 Users Guide
are typically implemented in-band from ESX to a disk array. ESX extensions to make use of
these primitives are collectively referred to as vStorage APIs for Array Integration (VAAI).
2.2 About 3PAR VAAI Plug-in 1.1.0 for VMware vSphere 4.1
To keep up with new advances in cloud computing, enhanced capabilities are required by the
SCSI layer stack so that SCSI can meet the demands of emerging virtualized infrastructures.
There are currently a number of shortcomings that need to be solved:
■ VMs competing for the same resources. In cloud computing environments, competition
for system resources can limit scalability and performance. While this resource contention is
rarely an issue in smaller environments, large ESX or vSphere servers that can host tens if
not hundreds of VMs may run up against these system scalability limits.
In these situations, the SCSI reservation bit locks a LUN when, for example, VMDK clones
are made. This precludes large environments from putting large numbers of VMDKs on a
single large LUN since other VMDKS on that LUN are negatively impacted waiting for a SCSI
reservation to complete while a clone is made of that VMDK file.
■ Expediting the creation of VMware initiated VMDK clones. VMware also has the
ability to create its own clones. However, this adds extra overhead to the ESX or vSphere
underlying physical server's CPU, memory and network resources since the clone has to
traverse the storage array, the host and then go back out to the storage array again.
■ Host overhead associated with zeroing out previously allocated space. vSphere
includes the ability to zero out blocks of data when storage is allocated to a VM. By first
zeroing out these blocks of data, it prevents the new VM from accidently accessing any of
the data that may have been stored on that disk by a deleted VM that previously had access
to it. However the new problem that results is that the newly created VM has to generate
excessive amounts of write I/O and overhead on the physical host and network in order to
zero out newly allocated blocks.
It is these storage specific issues that the vStorage APIs for Array Integration (VAAI) for vSphere
4.1 and the latest release of 3PAR's InForm OS resolve. By adding three new SCSI commands to
the standard SCSI command set, VMware and 3PAR provide virtualized data centers a more
granular control for scaling virtualized infrastructures. Following are descriptions for these
new commands.