The notion that a single converged data centre network makes for fewer switches and ports, resulting in a simpler network consuming less power and cooling, is flawed, according to Gartner.

Gartner research shows that a converged data centre network requires more switches and ports, is more complex to manage and consumes more power and cooling than two well-designed separate networks.
"The industry is abuzz with the promise of a single converged network infrastructure, this time in the data centre core," says Joe Skorupa, research vice-president at Gartner. "Alternatively described as fibre channel over ethernet (FCoE), data centre ethernet (DCE), or more precisely, data centre bridging (DCB), this latest set of developments hopes to succeed where InfiniBand failed in its bid to unify computing, networking and storage networks."
"The promise that a single converged data centre network would require fewer switches and ports doesn't stand up to scrutiny," says Skorupa. "This is because as networks grow beyond the capacity of a single switch, ports must be dedicated to interconnecting switches. In large mesh networks, entire switches do nothing but connect switches to one another. As a result, a single converged network actually uses more ports than a separate local area network (LAN) and storage area network (SAN). Additionally, since more equipment is required, maintenance and support costs are unlikely to be reduced."
In addition to the financial barriers to the success of a single converged data centre network, Gartner also says there are significant design and management issues to be addressed. When two networks are overlaid on a single infrastructure, complexity increases significantly. As traffic shares ports, line cards and inter-switch links, avoiding congestion (hot spots) becomes extremely difficult. Mr Skorupa said that over time, emerging standards, such as transparent interconnection of lots of links (TRILL) may make it easier to avoid these hot spots, but mature, standards-compliant implementations are at least two to three years away.
Debugging problems in the converged network are also more difficult since interactions between the LAN and SAN traffic can make root cause analysis more difficult. Since many problems are transient in nature, events must be correlated across the two virtual networks, increasing complexity. Should an outage be required for solving a problem or simply for performing maintenance, a downtime window that is acceptable for both environments may be required. This increases complexity and may increase cost, as well.
"It's clear that the barriers to a single network range from a dearth of available products and the price premium charged for those products to the requirement to "forklift upgrade" your entire network to long-standing organisational conflicts," says Skorupa. "However, while the promise that a unified fabric will require fewer switches and ports, resulting in a simpler network that consumes less power and cooling, may go unfulfilled, that doesn't mean that organisations should forgo the benefits of a unified network technology."
Skorupa says there is clear benefit in standardising on a single technology for all data centre networking if that technology adequately supports the needs of applications. This will simplify acquisition, training and sparing. However, settling on a single technology does not require that the networks be combined. Design, operations and troubleshooting is much easier with two separate networks, and it may also cost less to build two separate networks.