VIOS

From AIXWiki

VIOS = Virtual Input Output Server (also seen as VIO server or VIO)

The VIOS is a special LPAR that serves virtual I/O devices to other LPARs on the physical server. It is possible to run multiple VIO servers on a single system. Best practice dictates that at least 2 VIO servers are used per system to create redundancy. It is possible to assign a single SAN storage LUN to both VIO servers which then both present the LUN to a single LPAR. The net effect is that if one VIO fails or is taken off-line, the LPAR that uses the disk will not fail itself. The same technique can be applied to ethernet adapters.