Guest Operating System Storage Considerations

The virtual storage adapter presented to the guest operating system can influence storage performance, as can that device's driver, driver settings, and other factors within the guest. This section addresses those considerations.

• For most guest operating systems, the default virtual storage adapter in VMware Cloud on AWS is either LSI Logic Parallel or LSI Logic SAS, depending on the guest operating system and the virtual hardware version. However, VMware Cloud on AWS also includes a paravirtualized SCSI storage adapter, PVSCSI (also called VMware Paravirtual). The PVSCSI adapter offers a significant reduction in CPU utilization as well as potentially increased throughput compared to the default virtual storage adapters, and is thus the best choice for environments with very I/O-intensive guest applications.

  Note:

  In order to use PVSCSI, your virtual machine must be using virtual hardware version 7 or later, as described under ESXi General Considerations.

  Note:

  PVSCSI adapters are supported for boot drives in only some operating systems. For additional information see VMware KB article 1010398.

• If you choose to use the BusLogic Parallel virtual SCSI adapter, and are using a Windows guest operating system, you should use the custom BusLogic driver included in the VMware Tools package.

• The Non-Volatile Memory Express (NVMe) virtual storage adapter (virtual NVMe, or vNVMe) allows recent guest operating systems that include a native NVMe driver to use that driver to access storage through VMware Cloud on AWS. Compared to virtual SATA devices, the vNVMe virtual storage adapter accesses local PCIe SSD devices with much lower CPU cost per I/O and significantly higher IOPS.

• The depth of the queue of outstanding commands in the guest operating system SCSI driver can significantly impact disk performance. A queue depth that is too small, for example, limits the disk bandwidth that can be pushed through the virtual machine. See the driver-specific documentation for more information on how to adjust these settings.

• In some cases large I/O requests issued by applications in a virtual machine can be split by the guest storage driver. Changing the guest operating system’s registry settings to issue larger block size I/O requests can eliminate this splitting, thus enhancing performance. For additional information see VMware KB article 9645697.

• Make sure the disk partitions within the guest are aligned. For further information you might want to refer to the literature from the operating system vendor regarding appropriate tools to use as well as recommendations from the array vendor.

• VMware Cloud on AWS uses drives with 4KB sector size (that is, 4KB native, or 4Kn), but presents storage to the guest with 512B sector size (512 native). You can obtain the best storage performance if your workload issues mostly 4K-aligned I/Os. For more information on this subject, see VMware KB article 2091600 or Device Sector Formats in the vSphere Storage Guide. See SQL Server Configuration for specific recommendations for SQL Server.