We've been pondering a question that none of the vendors we queried is talking about: Do SMBs (small and midsize businesses) typically need SANs at all? The subtle message emanating from the Fibre Channel community and counterparts in the iSCSI world is that storage fabric topologies are the universal answer to DAS (direct-attached storage) issues.
There are two problems with this thinking.
First, none of the storage topologies in use today -- whether DAS, NAS (network-attached storage) or SANs -- are, in fact, truly networked storage. Why? The best definition of a network we have right now is the OSI (Open Systems Interconnection) model, which defines layers of functionality in a full network protocol. Not even TCP/IP, which adheres to this model more closely than Fibre Channel, complies with it fully. A truly networked storage topology would comprise an any-to-any configuration of nodes communicating on a peer basis with no single point of management -- a lot like the Internet.
Instead, current storage topologies are all forms of direct-attached storage: DAS is the direct attachment of storage to server, NAS is a thin-server OS bolted to an array, and SANs are switched server-attached storage. In truth, iSCSI doesn't create a storage network either; it's a channel protocol operated over a network interface. But iSCSI moves us closer to networked storage by using TCP/IP as a transport.
It's a Zen riddle, really: All storage is networked by virtue of the fact that applications access storage from servers attached to a network, the LAN. Yet no storage is networked nowadays because it all remains direct-attached. You figure it out, Grasshopper.
That said, we find it curious that over the past five years, DAS has become the whipping boy of storage vendors. To be sure, the direct attachment of storage arrays to servers has its foibles, including data-accessibility limitations, impediments to virtualization and management, and a disruptive scaling model. Fabrics address these problems, in theory at least, by breaking the hardwired storage-server relationship and creating an infrastructure that can deliver "a drink of storage" to any application that needs it. We say "in theory" because the market-share leaders in the FC SAN world today recommend that "zones" (switch-software-based aggregations of servers and storage targets) be defined on a single initiator (server)/single target (array) basis. This once again establishes a one-to-one relationship between servers and arrays, which, while perhaps making sense from a performance perspective, defeats the purpose.
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