Datasheet

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VMw a r e Pa r a V i r t u a l i z e d ScSi
Early versions of ESX supported virtual SCSI adapters that emulated BusLogic and LSI Logic
hardware storage adapters. This full virtualization provided broad compatibility with guest
operating systems supported by ESX. However, this prevents ESX from taking advantage of
performance optimizations that can be achieved with paravirtualized devices such as VMXNET
network adapters. vSphere introduces a new virtual storage adapter called PVSCSI, as shown in
Figure 1.9, which extends to the storage stack performance gains typically associated with other
paravirtual devices. In that respect, the PVSCSI adapter is similar to the paravirtualized net-
work adapter VMXNET that is available in ESX. As with other paravirtual devices, the PVSCSI
adapter improves I/O efficiency by using optimizations such as batching the processing of I/O
requests and I/O completion interrupts and reducing the cost of virtual interrupts. The PVSCI
adapter also benefits from a reduced number of context switches between the guest operating
system and ESX virtual machine monitor.
Figure 1.8
Creating a thin-
provisioned virtual
hard disk
Figure 1.9
Paravirtualized
SCSI controller
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