8 Gbps Fibre Channel promises bandwidth and data storage port boost

8 Gbps Fibre Channel promises to double bandwidth and boost the number of hosts connected to the SAN fabric, but will it put increased strain on data centre power and cooling?

8 Gbps Fibre Channel (FC) promises to double the speed of storage-area network (SAN) traffic and the number of hosts that can connect to a data storage port. In turn, this will potentially mean a smaller SAN hardware footprint and lower data centre costs. But will this come at the cost of increased data centre power and cooling costs?

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SearchStorage.co.UK: What is 8 Gbps Fibre Channel and what are its benefits?

Pinder: 8 Gbps Fibre Channel is the latest release of the Fibre Channel specification and allows devices to communicate at speeds of up to 8 Gbps. As one byte consists of 8 bits, this speed is equivalent to 800 MB per second.

The benefit of 8 Gbps FC in its most simple form is that it is able to transmit twice the amount of data over a single cable than was possible over the previous 4 Gbps standard. This will only be achieved, however, when you attach devices that comply with the 8 Gbps standard and are capable of transmitting data at this rate.

Organisations will therefore benefit when the next generation of SAN switches and storage arrays are manufactured and deployed with 8 Gbps ports. Once these units are incorporated into storage networks, they will allow twice the number of hosts to connect to a single data storage port -- without causing a bottleneck -- than was possible before.

This condensing of performance will ultimately lead to a lower footprint requirement for storage networks and an associated reduction in data centre costs. Many existing multi-mode or single-mode cables will support the new 8 Gbps standard, although it is likely that many existing SAN environments will not.

SearchStorage.co.UK: When should I upgrade to 8 Gbps Fibre Channel?

Pinder: If an organisation has spent a large amount of money within the last two years deploying a 4 Gbps SAN it will probably be uneconomical to throw away this investment and upgrade to 8 Gbps. If the SAN is suffering from bottlenecks that 8 Gbps technology will alleviate, then it is probable that the SAN was incorrectly designed in the first place.

Generally, upgrades to 8 Gbps technology will take place during the standard rounds of hardware refreshes that take place within organisations. As there will be a significant price premium for 8 Gbps devices for some time, their deployment will have to be considered using standard cost/benefit analysis. Customers will have to decide whether the benefit is high enough to justify the extra cost and, if this is not the case, they will either deploy 4 Gbps technology or sweat the current assets a little bit longer until prices fall.

It is likely that new large-scale SAN deployments will mix 8 Gbps with lower speed technology. The 8 Gbps technology will be reserved for high-end storage arrays and core switches, with the remaining devices still being 4 Gbps or even 2 Gbps in some cases.

It should be noted that most hardware manufacturers will future-proof their core SAN devices to enable the installation of 8 Gbps blades when customers have the desire to take advantage of the speed increase offered and lower purchase prices.

There are a few challenges that are associated with 8 Gbps Fibre Channel, including:

Device placement -- As the speed of devices increases, the distance that they are able to safely transmit reduces. When SCSI technology was increasing speed it got to the point where the safe transmit distance between devices was down to a few metres. This made deploying large numbers of devices very difficult and, in many cases, prevented the use of safe cabling routes between these devices. With Fibre Channel technology we are not yet in a similar situation, but many existing data centres will have to assess whether the current locations of patch panels prevents the deployment of 8 Gbps devices on certain floor tiles.

Power usage and cooling -- As devices run faster they tend to generate more heat. It is highly likely that 8 Gbps devices will generate more heat than 4 Gbps devices, and consideration must be given to their placement. If an 8 Gbps switch blade were to generate more heat than the 4 Gbps blade it replaced, this may cause the switch to generate more heat than was safe for its rack location. Similarly, an 8 Gbps blade could consume more power than a 4 Gbps blade, with power constraints in the rack preventing the use of all blades in the chassis. If a move of the device was not practical, then the purchase of 8 Gbps blades over 4 Gbps blades could be a waste of money.

In this interview, UK bureau chief Antony Adshead speaks with Steve Pinder, principal consultant at GlassHouse Technologies (UK), about the benefits and challenges associated with 8 Gbps Fibre Channel and when is the best time to upgrade from 4 Gbps Fibre Channel.

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