RAID (Redundant Array of Inexpensive Disks) are widely used in storage servers. Level-5 RAID is one of the most popular RAID architectures. Numerical analysis of exact Markovian dependability models of level-5 RAID architecture with orthogonal organization is unfeasible for many realistic model parameters due to the size of the resulting state space. In this paper we develop approximate dependability models for a level-5 RAID architecture with orthogonal organization which have small state spaces. We consider two measures: the steady-state unavailability and the unreliability. The models encompass disk hot spares and imperfect disk reconstruction. Using bounding techniques we analyze the accuracy of the models and show that the models are extremely accurate.