Pada saat kita membuat sebuah virtual machine di sebuah ESX maka secara default kita akan diberikan vSCSI controller. Biasanya defaultnya adalah LSI Logic SAS atau kadang LSI Logic Parallel. Secara umum, keduanya mencukupi dan kompatibel dengan hampir semua OS guest yang akan diinstall, baik Windows maupun Linux. Jika kita menginginkan vSCSI controller yang lebih mendukung pada IOPS yang tinggi alias high performance, maka sebaiknya kita mempertimbangkan untuk menggunakan VMware Paravirtual SCSI (a.k.a PVSCSI). Secara kasat mata, performance VM akan mengalami peningkatan up to 20% (dari beberapa studi dan eksperimen).

Secara umum, pilihan vSCSI controller sebagai berikut :

Berikut penjelasan untuk masing-masing pilihan SCSI controller :

• BusLogic – this was one of the first emulated vSCSI controllers available in the VMware platform.  The earliest versions of Windows has this driver available by default which made it easy when installing that particular OS. It wasn’t however as performant as the LSI Logic driver since Windows’ driver was limited to a queue depth of 1, so often one would manually load the LSI Logic driver instead.  While still available and used occasionally (Is anyone still running Win2K?), it should be considered legacy.
• LSI Logic Parallel (formerly knows as just LSI Logic) – 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.
• 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 or newer.
• 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.

Namun ada beberapa yang mesti diingat. PVSCSI memiliki beberapa limitasi :

• Hot add or hot remove requires a bus rescan from within the guest.
• Disks with snapshots might not experience performance gains when used on Paravirtual SCSI adapters if memory on the ESX host is over committed.
• Do not use PVSCSI on a virtual machine running Windows with spanned volumes. Data may become inaccessible to the guest operating system.
• If you upgrade from RHEL 5 to an unsupported kernel, you might not be able to access data on the virtual machine’s PVSCSI disks. You can run vmware-config-tools.pl with the kernel-version parameter to regain access.
• If a virtual machine uses PVSCSI, it cannot be part of a Microsoft Cluster Server (MSCS) cluster.

Semoga membantu.