Information Technology Reference
In-Depth Information
Table 6.3:
Virtual SCSi and SATA storage adapters in vSphere 5.5
(continued)
VM
Hardware
Versions
Supported
Virtual
Storage
Adapter
Description
LSI Logic parallel
4, 7, 8, 9, 10
h e LSI Logic parallel SCSI virtual adapter is well suited for and
well supported by newer guest OSes. Both LSI Logic controllers
provide equivalent performance.
LSI Logic SAS
7, 8, 9, 10
h e LSI Logic SAS controller is a better choice than LSI Logic paral-
lel when the guest OS is phasing out support for parallel SCSI in
favor of SAS. Performance between the two controllers is
equivalent.
VMware
Paravirtual
7, 8, 9, 10
h e VMware Paravirtual SCSI adapter is a virtualization-
optimized controller that provides higher throughput with lower
CPU overhead but at the cost of guest OS compatibility.
As you can see from Table 6.3, two of these adapters—the LSI Logic SAS and VMware
Paravirtual—are available only for VM hardware version 7 or higher. The LSI Logic SAS control-
ler is the default SCSI adapter suggested for VMs running Windows Server 2008 and 2008 R2,
while the LSI Logic parallel SCSI controller is the default for Windows Server 2003. Many of the
various Linux l avors default to the BusLogic parallel SCSI adapters.
The BusLogic and LSI Logic controllers are pretty straightforward; they emulate a known
SCSI controller. The AHCI adapter is a SATA-based controller to replace the older IDE adapter.
Typically this would only be used to support guest virtual CD-ROM drives. The VMware
Paravirtual SCSI adapter, though, is a different kind of controller.
In short, paravirtualized devices (and their corresponding drivers) are specii cally optimized
to communicate more directly with the underlying VM Monitor (VMM); they deliver higher
throughput and lower latency, and they usually signii cantly lower the CPU impact of the I/O
operations. This is the case with the VMware Paravirtual SCSI adapter in vSphere. We'll discuss
paravirtualized drivers in greater detail in Chapter 9.
Compared to other virtual SCSI adapters, the paravirtualized SCSI adapter shows improve-
ments in performance for virtual disks as well as improvements in the number of IOPS deliv-
ered at any given CPU utilization. The paravirtualized SCSI adapter also shows improvements
(decreases) in storage latency as observed from the guest OS.
If the paravirtualized SCSI adapter works so well, why not use it for everything? Well, for
one, this is an adapter type that exists only in vSphere environments, so you won't i nd the driv-
ers for the paravirtualized SCSI adapter on the install disk for most guest OSes. In general, we
recommend using the virtual SCSI adapter suggested by vSphere for the boot disk and the para-
virtualized SCSI adapter for any other virtual disks, especially other virtual disks with active
workloads.
