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Using SANs and NAS by W. Curtis Preston

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SAN Issues to Be Managed

There is no question that SANs bring significant advancements to the storage industry. However, taking advantage of this technology requires a major shift in how you think about and manage your storage. On one hand, Fibre Channel, the technology on which most SANs are based, is simply a new physical layer upon which SCSI data can travel. On the other hand, Fibre Channel has broken the SCSI mold in so many ways that it challenges a number of assumptions many of us have had for years about our SCSI-based storage devices. Since some of these assumptions are no longer true, it creates new issues that must be addressed—issues that must be managed.

Access to storage resources in a Fibre Channel network is accomplished using channels (thus the name Fibre Channel) through a loop (arbitrated loop), or a fabric (a network of SAN fabric switches) to connect one or more hosts to one or more storage devices. Each individual channel, or data path, in a SAN provides a virtual end-to-end connection between a server or host through the SAN to any intended and assigned storage resource, including all physical components and logical connections. Each path can be thought of, both physically and logically, as a virtual representation of a singular SCSI connection or cable. However, unlike the SCSI cable, this cable can create a channel from any SAN-connected server to any SAN-connected storage device. This results in many interesting differences between SANs and parallel SCSI. ...

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