The transition to 8 Gbps Fibre Channel (FC) hardware in storage-area networks (SANs) is well underway. In most...
environments, the decision is not whether to buy 8 Gbps Fibre Channel over 4 Gbps, but when and where to deploy it.
Upgrading your Fibre Channel to 8 Gbps comes with many considerations and is much different than deploying an 8 Gbps SAN in an environment that has no FC installed. This upgrade could be the replacement of existing 1 Gbps, 2 Gbps or 4 Gbps Fibre Channel hardware, or the addition of 8 Gbps ports and devices.
Consider future bandwidth needs
"Fabric upgrades, like other IT infrastructure upgrades, are most often an incremental exercise," said Nitin Garg, product manager at Cisco Systems Inc. "So you'll want to know where to add first and where to put in the 'hooks' so you can add easily later. Run analysis tools on the fabric to get an updated picture of where you're using bandwidth today and to get some data to do an educated trending exercise." Server virtualization and solid-state drive (SSD) deployments can be good indicators of a potential need for future bandwidth.
"Keep an eye on transition costs and complexity when upgrading an existing infrastructure," advised Steve Zivanic, QLogic Corp.'s senior director of corporate marketing. "Create an infrastructure that can avoid overhead when the fabric is expanded, like paying for dedicated inter-switch links."
Overhead can be described as implementation costs that are over and above per-usable-port hardware and software costs. In addition to inter-switch links (ISLs), another example could be the effort required to reconfigure existing switches when the fabric is rebooted.
Director switches or edge switches?
"Upgrade the core first -- you don't have to have an end-to-end 8 Gbps infrastructure to justify the project," said Erik Pounds, product marketing manager at Brocade Communications Systems Inc. "The core needs to support bursting rates above what the edge 'steady state' throughput rates are."
8 Gbps core switches or director switches can enable better performance for 4 Gbps at the edge, as well as support oversubscription in a 4 Gbps fabric. "8 Gbps performance allows heavy consolidation and more density at the core, up to hundreds of wire-speed ports. This enables more scalability of the fabric with reduced ISL stress, resulting in lower fabric congestion," Pounds said.
8 Gbps pricing issues
The price for most 8 Gbps switches, on a per-port basis, is essentially the same as 4 Gbps. This is due largely to the increase in adoption of the technology and the desire by vendors for the market to quickly settle on 8 Gbps Fibre Channel. On the host bus adapter (HBA) side, there is still somewhat of a price delta between 4 Gbps and 8 Gbps (depending on the manufacturer) due mainly to the cost differential of Small Form-Factor Plugs (SFPs).
The list price of 8 Gbps SFPs (which are different than previous generations) are higher than the 4 Gbps versions. But this delta will diminish as 8 Gbps adoption grows, which it did in 2009, when the 8 Gbps share of Fibre HBAs increased to almost 33%.
Hardware vendors are addressing pricing to make this less of an issue right now and most recommend that users make sure that SFPs are included in the quoted configurations. Most switches come loaded with SFPs, but some allow you to purchase them from a third party. Some vendors allow mixing of 4 Gbps and 8 Gbps SFPs in the same switch, which can also lower upfront costs.
The bottom line on price is that 8 Gbps Fibre Channel is getting very close to a "wash" with 4 Gbps, if it's not there already. Cabling issues are also a non-factor because it's on the same LC connector.
NPIV and NPV enable virtualization, reduce management complexity
N_Port ID Virtualization (NPIV) and N_Port Virtualization (NPV) can enable the virtualization of host and switch ports while reducing management complexity in larger or mixed SAN environments.
NPIV allows a single HBA (called an "N_Port") to register multiple World Wide Port Names (WWPNs) and N_Port ID numbers. This enables multiple virtual machines on a single host to have unique Port IDs on a SAN for zoning and LUN allocation. The only requirement is that the switch must also support NPIV.
NPV enables a switch port to present as an NPIV host to another switch. This can make the entire switch look like a single NPIV port and facilitate SAN expansion without consuming additional domain IDs or adding to management overhead. Some vendors also enable encryption of these links between fabrics, good for securing campus connections between data centers or on a MAN. Again, the only requirement is that the existing switches support NPIV.
8 Gbps Fibre Channel in mixed environments
The Fibre Channel standard has smoothed out potential interoperability issues, so you should be able to successfully add new 8 Gbps hardware from a different vendor. 8 Gbps ports and HBAs will also auto-negotiate down when operating in a 4 Gbps environment. But there are still some details that should be considered.
The existing fabric management software may not provide the same functionality with another vendor's hardware that you're used to with your existing SAN. Also, the support experience for a mixed-vendor SAN may be different than it was with one vendor.
BIO: Eric Slack is an analyst at Storage Switzerland
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