The Zen Riddle of Storage Networking

Networked storage is something of a Zen riddle today. On the one hand, it can be argued rather persuasively that all storage is already networked, whether that storage is provided by disks installed inside a server chassis, or mounted in arrays connected to a server via a SCSI parallel cable, or accessed across a LAN using a network file system protocol, or inter connected with other arrays and servers using a Fibre Channel switched fabric.

The justification for this claim is simple: In the prevailing open systems computing architecture of today, client/server, virtually all clients (applications or end-users) access data via servers that are themselves connected within a local- or wide-area internetwork (including the Internet). As shown in Figure 5-1, the overwhelming preponderance of storage requests are made and fulfilled across IP-based networks. So, effectively speaking, all storage is already networked.

Figure 5-1. Zen riddle: All storage is networked . . . across an IP network.

Conversely, it can be argued that no storage today is truly networked storage. The case can be made that it is inappropriate to use the term "networked storage" to describe any of the current classes of storage products and topologies. In point of fact, all of the so-called networked storage products perpetuate server-attached models.

For example, network-attached storage (NAS) is little more than a thin server operating system bolted on to a storage array. In even its most deliberate manifestation, in which the NAS operating system is custom-developed by its manufacturer (see Figure 5-2), the NAS thin server is basically a general purpose OS kernel that has been "optimized" to perform certain networking and storage- related tasks . Some inexpensive NAS devices, in fact, utilize general-purpose operating system kernels embedded on off-the-shelf silicon chips as their " brains ." Any way you view it, the NAS appliance is server-attached storage.

Figure 5-2. Network-attached storage operating system components .

The same argument, that networked storage is a misnomer, holds true in the case of storage arrays arranged in Fibre Channel fabrics . While it is true that Fibre Channel enables more devices to be interconnected and made accessible to a server than does its progenitor, the parallel SCSI bus, and, by consequence, that this capability enables nondisruptive scaling of the storage platform (within vendor-specific limits), the implementations made of FC fabrics today are not, technically speaking, networks. Placing a Fibre Channel switch between a server-attached storage device and its server host does not create networked storage, but merely switched, server-attached storage (see Figure 5-3).

Figure 5-3. Zen riddle: No storage is networked.

The distinction may seem to be an unimportant one until you require network services that are not usually implemented as a part of the function set of Fibre Channel Switches, such as standards-based in- band security or management. You must create workarounds to provide the necessary functionality.

As argued in the previous chapters, FCP itself was never intended to be a network protocol and contemporary FC fabrics are not networks in the traditional (International Standards Organization) definition of the word. A fabric cannot be substituted for a true network if storage is to be detached from a server and network-enabled.

Of course, the arguments advanced by both the "all-storage-is-networked-storage" and the "no-storage-is-networked-storage" crowds fly in the face of "conventional wisdom," which has been purchased at a price of tens of millions of marketing dollars spent by storage vendors annually. These perspectives also call into question the nice neat categories used by leading IT research and analysis companies to describe the storage industry. Even the moniker of the leading industry advocate, the Storage Networking Industry Association (SNIA), must be taken as part of the hype.

In the case of analysts, many of whom derive significant income streams from the vendor community, networked storage has become embedded as a product category. In an apparent homage to the "natural system" advanced by Carolus Linneaus (also known as Carl Linn ), analysts have set forth a taxonomy for the storage world consisting of two "kingdoms": server-attached storage and networked storage. Within the networked storage kingdom, they define two major phyla : NAS for file-oriented storage, and SAN for block-oriented storage (see Figure 5-4).

Figure 5-4. A contemporary storage taxonomy.

If one accepts that the distinction between networked and server-attached storage is largely specious, the more interesting aspect of this taxonomy is the bifurcation it introduces between platforms optimized for block-level and file-level storage. Since no formal distinction exists in the world of server-attached storage, this division of storage platforms within the networked storage world may be worth exploring.