<Li> In - band the most complicated to design and code </Li> <P> There are two commonly available implementations of network - based storage virtualization, appliance - based and switch - based . Both models can provide the same services, disk management, metadata lookup, data migration and replication . Both models also require some processing hardware to provide these services . </P> <P> Appliance based devices are dedicated hardware devices that provide SAN connectivity of one form or another . These sit between the hosts and storage and in the case of in - band (symmetric) appliances can provide all of the benefits and services discussed in this article . I / O requests are targeted at the appliance itself, which performs the meta - data mapping before redirecting the I / O by sending its own I / O request to the underlying storage . The in - band appliance can also provide caching of data, and most implementations provide some form of clustering of individual appliances to maintain an atomic view of the metadata as well as cache data . </P> <P> Switch based devices, as the name suggests, reside in the physical switch hardware used to connect the SAN devices . These also sit between the hosts and storage but may use different techniques to provide the metadata mapping, such as packet cracking to snoop on incoming I / O requests and perform the I / O redirection . It is much more difficult to ensure atomic updates of metadata in a switched environment and services requiring fast updates of data and metadata may be limited in switched implementations . </P>

What will be used by san to provide connectivity between hosts and storage