Within the SAN switch market, director-class switches are on the rise and the Fibre Channel (FC) SAN market is...
still healthy, despite a lot of talk about converged Ethernet and the notion that a single data centre networking platform could simultaneously act as a local-area network (LAN) and a storage-area network (SAN).
So what's driving demand for the high-capacity, resilient, chassis-based switches known as director-class switches?
Mike Murphy, a director of SNIA Europe, said the big driver for director-class switches is server virtualisation and consolidation. "With consolidation comes the need for higher-performance, higher-reliability switches," he said.
Analysts and vendors agree that the rise in SAN director-class switch use isn't just a case of users adding devices to their existing SAN fabrics; organisations are buying and installing new Fibre Channel SANs, as well as redesigning and rebuilding their current SANs to add more servers, more storage and more services — and SAN director-class switches are literally core to the plans of many who do this.
The dominance of Fibre Channel is clear when you compare 8 Gbps Fibre Channel with 10 Gbps Ethernet. Market research firm Dell'Oro Group estimates that 5.6 million high-speed switch ports shipped globally in 2009, and more than 60% were 8 Gbps Fibre Channel. That's a reversal from the previous year, when 10 Gbps Ethernet represented more than 60% of the 2.1 million high-speed switch ports shipped.
Research from Dell'Oro Group also shows record sequential worldwide sales growth for both modular and fixed Fibre Channel switches — roughly analogous to core and edge Ethernet switches — in the final quarter of 2009. Indeed, the market research company said the overall Fibre Channel SAN market, including switches and host bus adapters (HBAs) for servers, grew more than 15% quarter-on-quarter.
The benefits of director-class switches
Only Brocade and Cisco Systems offer true Fibre Channel director switches now, as between them they have consumed almost all of their rivals. Some market analysts define a wider category of chassis-based or modular switches, which also includes QLogic's stackable switches. While these can't match directors for scalability or resilience, they can still take a SAN significantly further than fixed switches alone.
The advantage of modular switches is the ability to start with a relatively low port count, then scale up as far as you need. It's possible to build large fabrics with fixed switches, but the need to dedicate switch ports to inter-switch links (ISLs) means that the fabric can become complex and unwieldy past a few dozen ports.
As a rule of thumb, if you are building a SAN that will scale to approximately 100 ports -- and whatever switches you build it with, it needs two redundant parallel fabrics, so that's only 50 server and storage connections -- you should design the core around modular or chassis-based switches. If it will scale to several hundred ports, then you need true director-class switches.
Director-class and modular switches bring greater -- and more scalable -- switching capacity than fixed switches, which is vital as organizations rapidly shift from 4 Gbps to 8 Gbps FC. A SAN director-class switch, such as Brocade's DCX SAN switch, offers 256 Gbps bandwidth per slot, allowing each slot to support 32 8 Gbps ports at full line rate with no oversubscription. And if you can structure your SAN to keep as much traffic as possible within the blade, it can switch it locally so there's less need for it to consume backplane bandwidth.
Director-class switches bring greater flexibility compared with fixed and low-end modular switches, as each chassis can house several blade types. These can be Fibre Channel over Ethernet (FCoE) blades for extending storage access to servers connected via Ethernet, blades for storage encryption or blades to connect two directors over a WAN for long-distance data replication.
Brocade DCX director-class switch helps law firm consolidate data centres
All of those considerations made director-class switches a natural choice for London-based global law firm Clifford Chance when it consolidated its data centres from multiple, multivendor, project-based storage infrastructures to a single SAN. The firm chose to go with Brocade's DCX devices, which gave it centralised management and 8 Gbps Fibre Channel, with a potential upgrade path to Converged Enhanced Ethernet (CEE) and FCoE.
A key factor was that the firm already had experience with both Fibre Channel and director-class switches, said Chris Turner, Clifford Chance's storage team leader. "The reason for getting the DCXs was to minimise the 'gotchas' in this project, as we had a track record of managing Brocade switches and 24000 Directors."
According to Turner, "the DCXs give us an increased switch density and allowed us to save power by removing a large number of old switches. They interconnect with all the operating systems and protocols we use, and are well proven throughout the industry, with excellent reliability records -- another definite requirement for a 'conservative' company's operations."
He added: "Reducing the number of switches and fabrics managed was obviously made easier with a switch capable of virtual fabric partitioning and channelling, and they allowed smooth SAN convergence by seamlessly connecting the old SANs to the new."
Turner noted that as large directors enable denser, more complex cores, SAN planning becomes more important. "Of course, we were in a headlong rush to utilise the DCXs almost from the day they were delivered," he said. "However, as in all projects of this type, careful planning is essential prior to commissioning, rather than going immediately to operations and running live applications."
Storage networking is clearly an area where there's a lot of development and a lot of "marketeering" being done -- especially around converged Ethernet schemes such as CEE and Cisco's Data Center Ethernet (DCE) equivalent. And if improved Ethernet works as advertised, it may diminish the need for Fibre Channel. But for now Fibre Channel is here and working, the technology is mature and well understood, and the skills are in place.