The VIOS is a specialized operating system that runs under a special type of logical partition (LPAR). It provides robust virtual storage and virtual network solution; when two or more Virtual I/O Servers are placed on the system, it also provides high availability capabilities between them.
A virtual i/o server is an appliance that provides virtual storage and shared ethernet adapter capability to client logical partitions. It allows a physical adapter with attached disks on the virtual i/o sever partition to be shared by one or more partitions, enabling clients to consolidate and potentially minimize the number of physical adapters required.
VSCSI and NPIV
VIOS provides two methods for delivering virtualized storage to the virtual machines (LPARs):
- Virtual SCSI target adapters (VSCSI)
- Virtual Fibre Channel adapters (NPIV)
VIOS is a special purpose partition that can serve I/O resources to other partitions. The type of LPAR is set at creation. The VIOS LPAR type allows for the creation of virtual server adapters, where a regular AIX/Linux LPAR does not.
– VIOS works by owning a physical resource and mapping that physical resource to virtual resources. Client LPARs can connect to the physical resource via these mappings.
– VIOS is not a hypervisor, nor is it required for sub-CPU virtualization. VIOS can be used to manage other partitions in some situations when a HMC is not used. This is called IVM (Integrated Virtualization Manager).
– Depending on configurations, VIOS may or may not be a single point of failure. When client partitions access I/O via a single path that is delivered via in a single VIOS, then that VIOS represents a potential single point of failure for that client partition.
– VIOS is typically configured in pairs along with various multipathing / failover methods in the client for virtual resources to prevent the VIOS from becoming a single point of failure.
– Active memory sharing and partition mobility require a VIOS partition. The VIOS partition acts as the controlling device for backing store for active memory sharing. All I/O to a partition capable of partition mobility must be handled by VIOS as well as the process of shipping memory between physical systems.