  One of the most important parts of cloud computing is storage devices, and
Redundant Array of Independent Disks (RAID) systems are well known and
frequently used storage devices. With the increasing production of data in
cloud environments, we need high-reliable storage, given the importance of
data. RAID system's reliability analysis is of particular significance in the
area of cloud storage. Generally, data redundancy is used to create fault
tolerance and increases the reliability of storage. This study has considered
three examples of the simple RAID storage models and analyzed their
reliability. All of which have a replication factor of two and have the same
number of disks and reliabilities. The only difference is the model that they
used for generating the redundancy. To compare these three models' reliability,
we examined the degree of fault tolerance (FT) and calculated the models'
reliability using the reliability block diagram (RBD). In this paper, the
effect of redundancy's type and the blocks' arrangement on the system's
reliability was investigated.
