Introduction-
To access virtual disks, a virtual machine uses virtual SCSI controllers. Each virtual disk that a virtual machine can access through one of the virtual SCSI controllers resides in the VMFS datastore, NFS-based datastore, or on a raw disk. The choice of SCSI controller does not affect whether your virtual disk is an IDE or SCSI disk.

Following virtual SCSI controllers commonly used…

A) BusLogic
– This was one of the first emulated vSCSI controllers available in the VMware platform.
– No updates and considered as legacy or for backward compatibility…

B) LSI Logic Parallel
– This was the other emulated vSCSI controller available originally in the VMware platform.
– Most operating systems had a driver that supported a queue depth of 32 and it became a very common choice, if not the default
– Default for Windows 2003/Vista and Linux

C) LSI Logic SAS
– This is an evolution of the parallel driver to support a new future facing standard.
– It began to grown popularity when Microsoft required its use for MCSC within Windows 2008 ore newer.
– Default for Windows 2008 or newer
– Linux guests SCSI disk hotplug works better with LSI Logic SAS
– Personally I use this
D) VMware Paravirtual (aka PVSCSI)
– This vSCSI controller is virtualization aware and was been designed to support very high throughput with minimal processing cost and is therefore the most efficient driver.
– In the past, there were issues if it was used with virtual machines that didn’t do a lot of IOPS, but that was resolved in vSphere 4.1.

* PVSCSI and LSI Logic Parallel/SAS are essentially the same when it comes to overall performance capability.
* Total of 4 vSCSI adapters are supported per virtual machine.  To provide the best performance, one should also distribute virtual disk across as many vSCSI adapters as possible
* Why not IDE? – IDE adapter completes one command at a time while SCSI can queue commands. So SCSI adapter is better optimized for parallel performance. Also Maximum of 4 IDE Devices per VM (includes CDROM) but SCSI allows 60 devices.

Thank You,
Arun

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