Limitations and restrictions of the Virtual I/O Server configuration

Learn about Virtual I/O Server (VIOS) configuration limitations.

Consider the following when implementing virtual Small Computer Serial Interface (SCSI):

• Virtual SCSI supports the following connection standards for backing devices: Fibre Channel, SCSI, SCSI RAID, iSCSI, SAS, SATA, USB, and IDE.
• The SCSI protocol defines mandatory and optional commands. While virtual SCSI supports all of the mandatory commands, not all of the optional commands are supported.
• There may be utilization implications when using virtual SCSI devices. Because the client/server model is made up of layers of function, using virtual SCSI can consume additional processor cycles when processing I/O requests.
• The VIOS is a dedicated logical partition, to be used only for VIOS operations. Other applications cannot run in the VIOS logical partition.
• If there is a resource shortage, performance degradation might occur. If a VIOS is serving many resources to other logical partitions, ensure that enough processor power is available. In case of high workload across virtual Ethernet adapters and virtual disks, logical partitions might experience delays in accessing resources.
• Logical volumes and files exported as virtual SCSI disks are always configured as single path devices on the client logical partition.
• Logical volumes or files exported as virtual SCSI disks that are part of the root volume group (rootvg) are not persistent if you reinstall the VIOS. However, they are persistent if you update the VIOS to a new service pack. Therefore, before reinstalling the VIOS, ensure that you back up the corresponding clients' virtual disks. When exporting logical volumes, it is best to export logical volumes from a volume group other than the root volume group. When exporting files, it is best to create file storage pools and the virtual media repository in a parent storage pool other than the root volume group.

Consider the following when implementing virtual adapters:

• Only Ethernet adapters can be shared. Other types of network adapters cannot be shared.
• IP forwarding is not supported on the VIOS.
• The maximum number of virtual adapters can be any value from 2 to 65,536. However, if you set the maximum number of virtual adapters to a value higher than 2048, the logical partition might fail to activate or the server firmware might require more system memory to manage the virtual adapters.

The VIOS supports client logical partitions running the following operating systems on the following POWER7® processor-based servers.