Intelligent Storage:The Big Picture

As traditional storage strategies become increasingly inadequate, new alternatives are rising to the challenge

By Arun Taneja

Continued from Page 2

What's Behind NAS and SAN?

SCSI. As I mentioned earlier, SCSI is the primary protocol used by servers in the enterprise to communicate with the storage devices, including disks, disk arrays, and tape libraries. It is extremely efficient and has stood the test of time. To complicate matters somewhat, SCSI is also the transport used by this protocol. So when SCSI devices talk to each other, they have everything they need to communicate with each other. Being a parallel protocol, however, SCSI suffers from serious limitations of distance, which has restricted its appeal to DAS where storage is attached over short distances, directly to the server. To implement SANs, which require the server- storage separation, you need a protocol that can span longer distances. Hence the creation of Fibre Channel.

Fibre Channel. FC is a transport protocol. It basically transports SCSI protocol that has been redefined to be serial, letting it carry over optical fiber media to distances of up to 10 km. The initial implementation of FC was at 100MBps (1 gigabit per second), with 200MBps devices now becoming available. Given these speed and distance specifications, you can implement a SAN with each server and storage unit - up to 10 km for the switch. You can interconnect the switches in a mesh to essentially create an infinitely complex fabric. In addition to carrying SCSI protocol, FC has also been defined to carry IP and other protocols. FC is really the only choice available today to build SANs and start reducing the horrendous costs of managing storage.

The advantages of FC are well understood: excellent bandwidth, long distances, and the ability to carry SCSI traffic - meaning no changes are required to thousands of applications that speak SCSI.

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The disadvantages are: interoperability issues primarily caused by vendor in-fighting and delayed creation of standards (a practical limitation, not an inherent technological one); requirements for implementing a new, separate network (all enterprises have Ethernet networks today that run TCP/IP); and the need to purchase a lot of new equipment.

Other technologies. For other related technologies, see the sidebar, "Storage Planning for the Future."

Storage Closure

The bottom line is: Storage needs are roughly doubling every year; storage management costs are spiraling out of control; the storage skill set is quite scarce; and traditional storage infrastructures are at a breaking point. SAN and NAS are excellent technologies to bring some order to this chaos. But selecting technologies is not easy. Should you jump into the fray with FC today, or wait for the iSCSI or InfiniBand panacea? My recommendation is simple: Jump in with both feet with FC right away because your needs are immediate, and the other technologies are not fully implemented yet. The good news is that many vendors are beginning to build bridge products from FCl to iSCSI or InfiniBand so your investment in FC will not go to waste. By starting now, you will gain experience with SANs and NAS and, no matter which technology gains momentum in future, you will be poised and ready. Without that experience, the storage tsunami is sure to drown those who do not act now.

Arun Taneja [arunt@enterprisestoragegroup.com, 508-482-0188] is a senior analyst with the Enterprise Storage Group, an analyst group focused on storage technologies. He has 25 years of experience in the storage and server industry.

RESOURCES

Cisco Systems
Compaq Computer Corp.
Dell Computer Corp.
EMC Corp.
Hewlett-Packard
IBM
Network Appliance Inc.
Sun Microsystems
Fibre Channel Industry Association
InfiniBand Trade Association
Internet Engineering Task Force Internet Draft for iSCSI
Storage Networking Industry Association