SAN/LAN/WAN Covergence Day One

In the first of a four part series on network convergence, Ian Yates looks at why convergence is on the IT agenda.

No matter what part of the network you call your own, somebody somewhere is suggesting you should converge. And the latest clarion call is to converge SANs with LANs and WANs.

Now if you're thinking the reason you installed a SAN in the first place was to keep the storage traffic separate from the other network traffic you'd be partly right, but it was the need for speed which first prompted the birth of SANs.

Ryan Perera from Nortel Networks explains how we ended up with a SAN in the first place. "Initially large enterprises started with what we call NAS, network attached storage," says Perera. And indeed the humble NAS solution is now finding favour with small business and consumers who have run out of room on their PCs with the explosion of digital music, photos and videos.

But for anything other than small networks, although the NAS concept ended the problem of finding extra hard drive slots in file servers, pretty soon the humble Ethernet access speed became intolerable.

"SANs became even more prominent because on top of the virtualisation of the storage resources, three other things came into the picture as well," says Perera. "Business connectivity, disaster recovery and replication applications, together made SANs even more prominent in the market place." And of course the SAN could use whatever high-speed link you could get your hands on without being restricted by the Ethernet of the day. The only restriction was the size of your budget, because the high-speed fibre channels preferred by SANs never made it to the low-cost commodity market.

When Ethernet made a quantum leap to 1Gbps speeds, and yet another giant leap to 10Gbps, the case for fibre channel started to look shaky as well as expensive. Dimension Data's Ronnie Altit explains: "At the end of the day fibre channel so far as SANs have communicated traditionally, is really just routing blocks of data and encapsulating them in fibre channel packets. So realistically all we're doing now is routing these same data packets in IP. We're wrapping them in IP packets."

So, it's certainly not rocket science at all and in fact it's a very cost effective way to share storage. "It saves having to buy $1,000 or $1,500 host bus adapters (HBAs) because people can now use the existing network," says Altit. "However, it's critical when implementing a fibre channel over IP network that the network itself is resilient. In a typical SAN environment one would configure it with multiple fibre channel switches and automatic fail over between one switch and another and multiple cards within servers so that servers can have a degree of availability for connecting to their storage. In an IP-based SAN, something similar needs to take place, so you've got to have that resilience at the LAN level such that you can ensure that your network is not going to become a point of failure."

This brings storage area network technology into the realms of the small business. "There's a large cost of entry into fibre channel networks and on that basis some organisations have been priced out of the market," says Altit. "Now actual storage costs, as we know, are certainly coming down but if we can couple that with connectivity costs coming down, then certainly we're in a better position." So that takes care of getting the speed you need for storage without paying the price for fibre channel, by using high speed Ethernet.

"As far as speed is concerned, most fibre channel installations that exist today on a SAN at a lot of organisations are probably only using 5% or 10% of the bandwidth that's available," says Altit. "Some organisations still have one gig fibre channels, some have two gig fibre channels and some are now moving to four gig. So if you have a one gig Ethernet network, often that's more than enough to be able to provide the connectivity at the required speed."

And 10Gbps Ethernet is already starting to be affordable, if you find you need a bit more speed to converge your SAN with your LAN. "10Gbps is going to become quite prolific over the next two to three years, then we're now comparing what's currently available on a fibre channel which is 4Gbps with 10Gbps," says Altit. "So whilst there may be some additional overhead for IP based traffic, that overhead is certainly going to be well and truly taken care of by the commensurate increase in bandwidth from a 1Gbps network to a 10Gbps network."


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